I have verified that this also occurs on 1.18.1 for x64 

2014-09-11 00:29:07 INFO juju.cmd supercommand.go:297 running juju-1.18.1-trusty-amd64 [gc]
2014-09-11 00:29:07 WARNING juju.cmd.juju common.go:40 ignoring environments.yaml: using bootstrap config in file "/home/botuser/.juju/environments/maas.jenv"
2014-09-11 00:29:07 DEBUG juju.environs open.go:86 ConfigForName found bootstrap config map[string]interface {}{"bootstrap-addresses-delay":10, "default-series":"trusty", "development":false, "logging-config":"<root>=WARNING;unit=DEBUG", "maas-server":"http://10.228.65.102/MAAS", "bootstrap-retry-delay":5, "syslog-port":6514, "tools-url":"", "api-port":17070, "authorized-keys":"ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQCeAr+6koYzHa/LCEKAFTLtbY1dOWTKVb+hUpLS8USCYn7ZmKF8a4i4cO6wCUIwAEEOLKSkGEJEHlXIwBXtfeT2CXgsTsDmC8FQh2CQoGBi/kFuQcKg1DMX7O3CQfRP1ZUGUH1+vpkf8qTzVKzl4X97G9XNQzbcugn2Uq4RvPU6A7PNwq3U6PANVjs2Xkf7xtJYCnKP94EP6cEjTkAUZSTu8llVGrbf7PnTt713RxoqfEOGKtVNylMPX0yBdXx/t20teUPhN3MQWflBLvSYvSWBYY3uwyaGUiTnR/7W77pJXZMvAntpdQlPhfb0DeJGgqeEQzuki+qlSuVkKi7cfPe3 juju-client-key\nssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQDlw9nRnWJnFZZ8/0cgbwSzbps3F9x3/vTlPhkalSPb08ArtaIbrgy7jubyBjzqEpF7G21hn0sVLPbZroRfAxIdzwFBlp4MomeCR1mmstFv3YmqKPtagRoDgvlaoqlSkl07rvLeVatemPzAz6Yx167JJq5zSgViaNOwdUu68e2XlaCyj4j4qnuGeBAklyDiRJzsH8Lzgh4fv2F+EbBFVYvWO0EW3e/emv9ubETWxsxTEYKh+Pp0xBzlFwavqUe/K64ksUgMM4X3ac67F+sTQnbLKoKfzpUZnPVcI/AIO5oh/vuVmyMbn25Dbia0TPNGIXrTKyOM90NN1SWQ+32QNUcV botuser@virt2\n", "firewall-mode":"instance", "https-proxy":"http://10.228.0.2:3128", "maas-oauth":"VqqdsvxD8Ykj5LmneH:TnLPvfXELAQU3XrYNA:D2e9s9dvnP3ffHBJuyQ2aj43eyV2M8T3", "type":"maas", "ca-cert":"-----BEGIN CERTIFICATE-----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\nT4urqVy7/s2/ht0g2ITjjKuHNQCE+i40hzMppx4=\n-----END CERTIFICATE-----\n", "http-proxy":"http://10.228.0.2:3128", "image-metadata-url":"", "admin-secret":"4d528e9fd6bc30c35c5457b703613824", "maas-agent-name":"25a9b1d7-ec16-44c2-8e12-942b9a9dacfe", "name":"maas", "state-port":37017, "tools-metadata-url":"", "bootstrap-timeout":600, "ca-private-key":"-----BEGIN RSA PRIVATE KEY-----\nMIICXAIBAAKBgQDMwDad8y3Jf5s1w2JAwzQRJ37YqWP+DCZmJvQ1gng+mhrnxVKv\n80jCtjcXDhrKulelWRJhbQDQ+zLKajxsrHS3WyffuByVel1uN3qE+S5Y44h2jFj/\nt59cByvmZPYSHvvRetBjf83/oya4QrVl71P9Uz8H3QVCxcbScvj58XVu/wIDAQAB\nAoGAFmTvlFcEqwVJ9JdqJ6syBq5LMWdViHPLv2CDVVbvz+kLCE6MvLHfQ2yqmdrx\nEztOWsdjO0Sw0iqnY3w7H6e9HB6KP40wxNbO20o+lOZkviTZeWK5eijjMZrKu1CM\nMVhClwnak9UjmX2oJQkhGzt1Dgueuygr5anM72HlFv/XIAECQQD8ZmOd11B7UFoP\nTfEU2o96Dt2jZ0ZtkzHAwPnsUuq8GfN2yiYNIdZnCak8gzggM/oHn7y6fmvRIoEN\nWatqu6u7AkEAz6vWsbAN3lkA+Ykt//uf7TPyMEVDfZITfWfZNhVfOiubSRwJdUOj\necT2aEMqgNQ+syp642rqwIyPuXZq6+97jQJAE4agQj+7/C41KWXwNprJ6rlnsBJ3\nQlbWzIChVQT9H9wqF5B/7RgnDAWVUBceqm8a8qgK46qQELfIoA3F0xX9rQJAG5pk\nnBOhlEdSSNjCA39nn3jDHUVnlh4/dvDBv12R3cKEDnCqlSqbZQkYE32x/ZO4jcn8\nsZO5hkRoqiciSR/41QJBANGioU/cNdqDTKncR9XF3M8yncXMpDDbshtiu2qsk5SQ\nzHnbq5BaDbdMU0QxGE+kAg/RlxhMxbhJhhmQTp4xOFE=\n-----END RSA PRIVATE KEY-----\n", "charm-store-auth":"", "image-stream":"", "ssl-hostname-verification":true, "test-mode":false}
2014-09-11 00:29:07 DEBUG juju.environs.configstore disk.go:64 Making /home/botuser/.juju/environments
2014-09-11 00:29:07 INFO juju.environs open.go:177 environment info already exists; using New not Prepare
2014-09-11 00:29:07 DEBUG juju.provider.maas environprovider.go:30 opening environment "maas".
2014-09-11 00:29:08 INFO juju.environs.bootstrap bootstrap.go:46 bootstrapping environment "maas"
2014-09-11 00:29:08 DEBUG juju.environs.bootstrap synctools.go:159 looking for bootstrap tools: series="trusty", arch=<nil>, version=<nil>
2014-09-11 00:29:08 INFO juju.environs.tools tools.go:186 filtering tools by released version
2014-09-11 00:29:08 INFO juju.environs.tools tools.go:86 reading tools with major.minor version 1.18
2014-09-11 00:29:08 INFO juju.environs.tools tools.go:97 filtering tools by series: trusty
2014-09-11 00:29:08 DEBUG juju.environs.tools tools.go:45 no architecture specified when finding tools, looking for any
2014-09-11 00:29:08 DEBUG juju.environs.simplestreams simplestreams.go:490 fetchData failed for "tools/streams/v1/index.sjson": file '25a9b1d7-ec16-44c2-8e12-942b9a9dacfe-tools/streams/v1/index.sjson' not found not found
2014-09-11 00:29:08 DEBUG juju.environs.simplestreams simplestreams.go:464 cannot load index "streams/v1/index.sjson": invalid URL "tools/streams/v1/index.sjson" not found
2014-09-11 00:29:08 DEBUG juju.environs.simplestreams simplestreams.go:490 fetchData failed for "tools/streams/v1/index.json": file '25a9b1d7-ec16-44c2-8e12-942b9a9dacfe-tools/streams/v1/index.json' not found not found
2014-09-11 00:29:08 DEBUG juju.environs.simplestreams simplestreams.go:464 cannot load index "streams/v1/index.json": invalid URL "tools/streams/v1/index.json" not found
2014-09-11 00:29:08 INFO juju.utils http.go:55 hostname SSL verification enabled
2014-09-11 00:29:09 INFO juju.utils http.go:55 hostname SSL verification enabled
2014-09-11 00:29:09 DEBUG juju.environs.simplestreams simplestreams.go:677 using default candidate for content id "com.ubuntu.juju:released:tools" are {20140910 mirrors:1.0 content-download streams/v1/cpc-mirrors.sjson []}
2014-09-11 00:29:09 INFO juju.utils http.go:55 hostname SSL verification enabled
2014-09-11 00:29:10 DEBUG juju.environs.simplestreams simplestreams.go:548 no mirror information available for { }: mirror info with cloud { } not found
2014-09-11 00:29:10 DEBUG juju.environs.simplestreams simplestreams.go:468 read metadata index at "https://streams.canonical.com/juju/tools/streams/v1/index.sjson"
2014-09-11 00:29:10 DEBUG juju.environs.simplestreams simplestreams.go:635 candidate matches for products ["com.ubuntu.juju:14.04:amd64" "com.ubuntu.juju:14.04:i386" "com.ubuntu.juju:14.04:armhf" "com.ubuntu.juju:14.04:arm64" "com.ubuntu.juju:14.04:ppc64"] are [{Wed, 10 Sep 2014 23:03:17 +0000 products:1.0 content-download  [] streams/v1/com.ubuntu.juju:released:tools.sjson [com.ubuntu.juju:12.04:amd64 com.ubuntu.juju:12.04:armhf com.ubuntu.juju:12.04:i386 com.ubuntu.juju:12.10:amd64 com.ubuntu.juju:12.10:i386 com.ubuntu.juju:13.04:amd64 com.ubuntu.juju:13.04:i386 com.ubuntu.juju:13.10:amd64 com.ubuntu.juju:13.10:armhf com.ubuntu.juju:13.10:i386 com.ubuntu.juju:14.04:amd64 com.ubuntu.juju:14.04:arm64 com.ubuntu.juju:14.04:armhf com.ubuntu.juju:14.04:i386 com.ubuntu.juju:14.04:powerpc com.ubuntu.juju:14.04:ppc64 com.ubuntu.juju:14.04:ppc64el com.ubuntu.juju:14.10:amd64 com.ubuntu.juju:14.10:arm64 com.ubuntu.juju:14.10:armhf com.ubuntu.juju:14.10:i386 com.ubuntu.juju:14.10:ppc64 com.ubuntu.juju:14.10:ppc64el]}]
2014-09-11 00:29:10 DEBUG juju.environs.simplestreams simplestreams.go:947 finding products at path "streams/v1/com.ubuntu.juju:released:tools.sjson"
2014-09-11 00:29:10 INFO juju.utils http.go:55 hostname SSL verification enabled
2014-09-11 00:29:11 DEBUG juju.environs.simplestreams simplestreams.go:985 metadata: &{map[com.ubuntu.juju:12.10:amd64:{ 1.15.0 amd64   map[20140910:0xc2101a6300]} com.ubuntu.juju:12.10:i386:{ 1.15.0 i386   map[20140910:0xc2101a68a0]} com.ubuntu.juju:13.04:amd64:{ 1.15.0 amd64   map[20140910:0xc210164060]} com.ubuntu.juju:13.04:i386:{ 1.15.0 i386   map[20140910:0xc210164180]} com.ubuntu.juju:14.04:ppc64:{ 1.18.4 ppc64   map[20140910:0xc2100f74e0]} com.ubuntu.juju:14.10:ppc64el:{ 1.18.4 ppc64el   map[20140910:0xc2101151e0]} com.ubuntu.juju:12.04:i386:{ 1.15.0 i386   map[20140910:0xc2101a6180]} com.ubuntu.juju:13.10:i386:{ 1.15.0 i386   map[20140910:0xc210164660]} com.ubuntu.juju:14.04:amd64:{ 1.16.2 amd64   map[20140910:0xc210164780]} com.ubuntu.juju:14.04:arm64:{ 1.17.2 arm64   map[20140910:0xc2101649c0]} com.ubuntu.juju:14.04:armhf:{ 1.16.2 armhf   map[20140910:0xc210164f00]} com.ubuntu.juju:14.04:powerpc:{ 1.17.2 powerpc   map[20140910:0xc2100f7300]} com.ubuntu.juju:14.10:amd64:{ 1.18.2 amd64   map[20140910:0xc210115420]} com.ubuntu.juju:14.10:arm64:{ 1.18.4 arm64   map[20140910:0xc210115960]} com.ubuntu.juju:14.10:armhf:{ 1.18.2 armhf   map[20140910:0xc210115b40]} com.ubuntu.juju:14.10:i386:{ 1.18.2 i386   map[20140910:0xc210115de0]} com.ubuntu.juju:12.04:amd64:{ 1.15.0 amd64   map[20140910:0xc2100f7ea0]} com.ubuntu.juju:12.04:armhf:{ 1.16.2 armhf   map[20140910:0xc2101a64e0]} com.ubuntu.juju:13.10:amd64:{ 1.15.0 amd64   map[20140910:0xc210164300]} com.ubuntu.juju:13.10:armhf:{ 1.16.2 armhf   map[20140910:0xc2101644e0]} com.ubuntu.juju:14.04:i386:{ 1.16.2 i386   map[20140910:0xc2100f7000]} com.ubuntu.juju:14.04:ppc64el:{ 1.17.2 ppc64el   map[20140910:0xc2100f7840]} com.ubuntu.juju:14.10:ppc64:{ 1.18.4 ppc64   map[20140910:0xc2101150c0]}] map[] Wed, 10 Sep 2014 23:03:17 +0000 products:1.0 com.ubuntu.juju:released:tools}
panic: invalid version "1.21-alpha1"

goroutine 1 [running]:
runtime.panic(0xbebf00, 0xc2105e6cb0)
	/usr/lib/go/src/pkg/runtime/panic.c:266 +0xb6
launchpad.net/juju-core/version.MustParse(0xc21020e510, 0xb, 0xc21015e140, 0xc21015e140, 0xc210325901, ...)
	/build/buildd/juju-core-1.18.1/src/launchpad.net/juju-core/version/version.go:151 +0x81
launchpad.net/juju-core/environs/tools.appendMatchingTools(0x7f0943598450, 0xc21015b210, 0xc2105e6c70, 0x1, 0x1, ...)
	/build/buildd/juju-core-1.18.1/src/launchpad.net/juju-core/environs/tools/simplestreams.go:224 +0x330
launchpad.net/juju-core/environs/simplestreams.GetLatestMetadata(0xc2102dc780, 0x7f0943598490, 0xc21015e140, 0x7f0943598450, 0xc21015b210, ...)
	/build/buildd/juju-core-1.18.1/src/launchpad.net/juju-core/environs/simplestreams/simplestreams.go:1023 +0x76c
launchpad.net/juju-core/environs/simplestreams.(*IndexReference).getLatestMetadataWithFormat(0xc210151480, 0x7f0943598490, 0xc21015e140, 0xd9f1d0, 0xc, ...)
	/build/buildd/juju-core-1.18.1/src/launchpad.net/juju-core/environs/simplestreams/simplestreams.go:986 +0x1a5
launchpad.net/juju-core/environs/simplestreams.getMaybeSignedMetadata(0x7f0943598450, 0xc21015b210, 0xdfa530, 0x10, 0x7f0943598490, ...)
	/build/buildd/juju-core-1.18.1/src/launchpad.net/juju-core/environs/simplestreams/simplestreams.go:469 +0x5e9
launchpad.net/juju-core/environs/simplestreams.GetMetadata(0xc21004d2a0, 0x2, 0x2, 0xdfa530, 0x10, ...)
	/build/buildd/juju-core-1.18.1/src/launchpad.net/juju-core/environs/simplestreams/simplestreams.go:426 +0x12e
launchpad.net/juju-core/environs/tools.Fetch(0xc21004d2a0, 0x2, 0x2, 0xdfa530, 0x10, ...)
	/build/buildd/juju-core-1.18.1/src/launchpad.net/juju-core/environs/tools/simplestreams.go:182 +0x16a
launchpad.net/juju-core/environs/tools.FindToolsForCloud(0xc21004d2a0, 0x2, 0x2, 0x0, 0x0, ...)
	/build/buildd/juju-core-1.18.1/src/launchpad.net/juju-core/environs/tools/tools.go:121 +0x15f
launchpad.net/juju-core/environs/tools.FindTools(0x7f0943598398, 0xc210115f60, 0x1, 0x12, 0x1, ...)
	/build/buildd/juju-core-1.18.1/src/launchpad.net/juju-core/environs/tools/tools.go:106 +0x5aa
launchpad.net/juju-core/environs/tools.FindBootstrapTools(0x7f0943598398, 0xc210115f60, 0x0, 0x0, 0xc21012ad88, ...)
	/build/buildd/juju-core-1.18.1/src/launchpad.net/juju-core/environs/tools/tools.go:189 +0x351
launchpad.net/juju-core/environs/bootstrap.EnsureToolsAvailability(0x7f0943594f88, 0xc2100ae820, 0x7f0943596cb8, 0xc210115f60, 0xc21012ad88, ...)
	/build/buildd/juju-core-1.18.1/src/launchpad.net/juju-core/environs/bootstrap/synctools.go:168 +0x2a6
launchpad.net/juju-core/provider/common.EnsureBootstrapTools(0x7f0943594f88, 0xc2100ae820, 0x7f0943596cb8, 0xc210115f60, 0xc21012ad88, ...)
	/build/buildd/juju-core-1.18.1/src/launchpad.net/juju-core/provider/common/bootstrap.go:407 +0x74
launchpad.net/juju-core/provider/common.Bootstrap(0x7f0943594f88, 0xc2100ae820, 0x7f0943596cb8, 0xc210115f60, 0x0, ...)
	/build/buildd/juju-core-1.18.1/src/launchpad.net/juju-core/provider/common/bootstrap.go:45 +0x16b
launchpad.net/juju-core/provider/maas.(*maasEnviron).Bootstrap(0xc210115f60, 0x7f0943594f88, 0xc2100ae820, 0x0, 0x0, ...)
	/build/buildd/juju-core-1.18.1/src/launchpad.net/juju-core/provider/maas/environ.go:87 +0x72
launchpad.net/juju-core/environs/bootstrap.Bootstrap(0x7f0943594f88, 0xc2100ae820, 0x7f0943596cb8, 0xc210115f60, 0x0, ...)
	/build/buildd/juju-core-1.18.1/src/launchpad.net/juju-core/environs/bootstrap/bootstrap.go:47 +0x5e3
main.(*BootstrapCommand).Run(0xc2100e6c00, 0xc2100ae820, 0xc21003fa90, 0x0)
	/build/buildd/juju-core-1.18.1/src/launchpad.net/juju-core/cmd/juju/bootstrap.go:143 +0x67f
main.envCmdWrapper.Run(0x7f0943593078, 0xc2100e6c00, 0xc2100ae820, 0x7f09433ed1d8, 0x2)
	/build/buildd/juju-core-1.18.1/src/launchpad.net/juju-core/cmd/juju/main.go:158 +0x48
main.(*envCmdWrapper).Run(0xc210036ff0, 0xc2100ae820, 0x14, 0x7f09433ed1d8)
	/build/buildd/juju-core-1.18.1/src/launchpad.net/juju-core/cmd/juju/addmachine.go:1 +0x9a
launchpad.net/juju-core/cmd.(*SuperCommand).Run(0xc2100e6b80, 0xc2100ae820, 0xc2100ae820, 0x0)
	/build/buildd/juju-core-1.18.1/src/launchpad.net/juju-core/cmd/supercommand.go:298 +0x439
launchpad.net/juju-core/cmd.Main(0x7f0943594ae0, 0xc2100e6b80, 0xc2100ae820, 0xc21000a010, 0x2, ...)
	/build/buildd/juju-core-1.18.1/src/launchpad.net/juju-core/cmd/cmd.go:244 +0x283
main.Main(0xc21000a000, 0x3, 0x3)
	/build/buildd/juju-core-1.18.1/src/launchpad.net/juju-core/cmd/juju/main.go:131 +0x439d
main.main()
	/build/buildd/juju-core-1.18.1/src/launchpad.net/juju-core/cmd/juju/main.go:173 +0x44

goroutine 3 [syscall]:
os/signal.loop()
	/usr/lib/go/src/pkg/os/signal/signal_unix.go:21 +0x1e
created by os/signal.init·1
	/usr/lib/go/src/pkg/os/signal/signal_unix.go:27 +0x31

goroutine 9 [runnable]:
main.func·002()
	/build/buildd/juju-core-1.18.1/src/launchpad.net/juju-core/cmd/juju/bootstrap.go:111 +0x45
created by main.(*BootstrapCommand).Run
	/build/buildd/juju-core-1.18.1/src/launchpad.net/juju-core/cmd/juju/bootstrap.go:114 +0x236

goroutine 32 [syscall]:
runtime.goexit()
	/usr/lib/go/src/pkg/runtime/proc.c:1394