This problem has re-appeared.

It's not exactly the same, it did it after a cold boot and I had a fight getting it working. Interfaces have unique mac addresses, but one or all of them remained unresponsive after a boot or a down/up.

Uname now: 2.6.32.16-141.fc12.i686
Picked this up in dmesg:
Aug  4 19:35:18 turnstile kernel: ------------[ cut here ]------------
Aug  4 19:35:18 turnstile kernel: WARNING: at net/sched/sch_generic.c:261 dev_watchdog+0xc6/0x158()
Aug  4 19:35:18 turnstile kernel: Hardware name:
Aug  4 19:35:18 turnstile kernel: NETDEV WATCHDOG: eth0 (r8169): transmit queue 0 timed out
Aug  4 19:35:18 turnstile kernel: Modules linked in: xt_multiport ipt_LOG act_nat ebt_dnat ebt_snat ebtable_nat ebtables iptable_nat nf_nat_snmp_basic nf_nat_proto_udplite nf_nat_sip nf_nat_irc nf_nat_ftp nf_nat_pptp nf_nat_proto_gre nf_nat_proto_dccp nf_nat_amanda nf_nat_proto_sctp libcrc32c nf_nat_tftp nf_nat_h323 nf_nat nf_conntrack_irc nf_conntrack_ftp nf_conntrack_netbios_ns ts_kmp nf_conntrack_amanda nf_conntrack_proto_udplite nf_conntrack_proto_sctp nf_conntrack_sip nf_conntrack_netlink nfnetlink nf_conntrack_tftp nf_conntrack_pptp nf_conntrack_proto_gre nf_conntrack_sane nf_conntrack_proto_dccp nf_conntrack_h323 nf_conntrack_ipv6 ip6t_LOG ip6table_filter ip6_tables cpufreq_ondemand acpi_cpufreq sit tunnel4 ipv6 dm_multipath uinput i2c_viapro i2c_core via_rhine r8169 mii pata_acpi ata_generic firewire_ohci sata_via firewire_core crc_itu_t [last unloaded: scsi_wait_scan]
Aug  4 19:35:18 turnstile kernel: Pid: 0, comm: swapper Not tainted 2.6.32.16-141.fc12.i686 #1
Aug  4 19:35:18 turnstile kernel: Call Trace:
Aug  4 19:35:18 turnstile kernel: [<c043a779>] warn_slowpath_common+0x6a/0x81
Aug  4 19:35:18 turnstile kernel: [<c071b7e1>] ? dev_watchdog+0xc6/0x158
Aug  4 19:35:18 turnstile kernel: [<c043a7ce>] warn_slowpath_fmt+0x29/0x2c
Aug  4 19:35:18 turnstile kernel: [<c071b7e1>] dev_watchdog+0xc6/0x158
Aug  4 19:35:18 turnstile kernel: [<c04475ae>] ? __mod_timer+0x115/0x120
Aug  4 19:35:18 turnstile kernel: [<c04410f8>] ? local_bh_enable_ip+0xd/0xf
Aug  4 19:35:18 turnstile kernel: [<c0795303>] ? _spin_unlock_bh+0x13/0x15
Aug  4 19:35:18 turnstile kernel: [<f7e423cd>] ? fib6_run_gc+0xb7/0xbe [ipv6]
Aug  4 19:35:18 turnstile kernel: [<c0447277>] run_timer_softirq+0x16d/0x1f0
Aug  4 19:35:18 turnstile kernel: [<c071b71b>] ? dev_watchdog+0x0/0x158
Aug  4 19:35:18 turnstile kernel: [<c0440e72>] __do_softirq+0xb1/0x157
Aug  4 19:35:18 turnstile kernel: [<c0440f4e>] do_softirq+0x36/0x41
Aug  4 19:35:18 turnstile kernel: [<c0441041>] irq_exit+0x2e/0x61
Aug  4 19:35:18 turnstile kernel: [<c0404e3d>] do_IRQ+0x86/0x9a
Aug  4 19:35:18 turnstile kernel: [<c0403c90>] common_interrupt+0x30/0x38
Aug  4 19:35:18 turnstile kernel: [<c0617074>] ? acpi_idle_enter_simple+0x10f/0x142
Aug  4 19:35:18 turnstile kernel: [<c0616da5>] acpi_idle_enter_bm+0xc7/0x287
Aug  4 19:35:18 turnstile kernel: [<c06e785c>] cpuidle_idle_call+0x73/0xcb
Aug  4 19:35:18 turnstile kernel: [<c0402728>] cpu_idle+0x96/0xb2
Aug  4 19:35:18 turnstile kernel: [<c0782a1c>] rest_init+0x58/0x5a
Aug  4 19:35:18 turnstile kernel: [<c09da8dd>] start_kernel+0x33c/0x341
Aug  4 19:35:18 turnstile kernel: [<c09da09e>] i386_start_kernel+0x9e/0xa5
Aug  4 19:35:18 turnstile kernel: ---[ end trace 58bb370737c8d652 ]---

What's going on ?