[2.1] After upgrade to latest trunk (pre-beta1) and after updating images, machines fail to pxe boot due to missing hwe-x kernel

I've upgraded from a previous MAAS version. The previous version was using old MAAS images (v2) and were using hwe-t as the default kernel. After the upgrade my machines failed to PXE boot and they are showing the following messages in event log:

Queried node's BMC - Power state queried: on Fri, 30 Sep. 2016 19:51:22
Node changed status - From 'Commissioning' to 'Failed commissioning' Fri, 30 Sep. 2016 19:51:01
Marking node failed - Missing boot image ubuntu/amd64/hwe-x/xenial. Fri, 30 Sep. 2016 19:51:01
TFTP Request - ubuntu/amd64/hwe-x/xenial/no-such-image/boot-kernel Fri, 30 Sep. 2016 19:51:01
PXE Request - commissioning

Note that i did not set a min kernel, nor a default kernel. It was just a stock install without making any chances:

==> /var/log/maas/rackd.log <==
2016-09-30 19:56:10 [ClusterClient,client] RemoteOriginReadSession starting on 33281
2016-09-30 19:56:10 [ClusterClient,client] Starting protocol <tftp.bootstrap.RemoteOriginReadSession object at 0x7f7319f38780>
2016-09-30 19:56:10 [RemoteOriginReadSession (UDP)] Final ACK received, transfer successful
2016-09-30 19:56:10 [-] (UDP Port 33281 Closed)
2016-09-30 19:56:10 [-] Stopping protocol <tftp.bootstrap.RemoteOriginReadSession object at 0x7f7319f38780>
2016-09-30 19:56:10 [TFTP (UDP)] Datagram received from ('10.90.90.201', 49155): <RRQDatagram(filename=b'ubuntu/amd64/hwe-x/xenial/no-such-image/boot-k
ernel', mode=b'octet', options=OrderedDict([(b'tsize', b'0'), (b'blksize', b'1408')]))>

==> /var/log/maas/maas.log <==
Sep 30 19:56:10 maas00 maas.node: [INFO] nuc01: Status transition from COMMISSIONING to FAILED_COMMISSIONING
Sep 30 19:56:10 maas00 maas.node: [ERROR] nuc01: Marking node failed: Missing boot image ubuntu/amd64/hwe-x/xenial.

ubuntu@maas00:~$ ls -l /var/lib/maas/boot-resources/current/ubuntu/amd64/
total 68
drwxr-xr-x 4 maas maas 4096 Sep 30 19:35 ga-16.04
drwxr-xr-x 3 maas maas 4096 Sep 30 19:35 ga-16.04-lowlatency
drwxr-xr-x 3 maas maas 4096 Sep 30 19:35 ga-16.10
drwxr-xr-x 3 maas maas 4096 Sep 30 19:35 ga-16.10-lowlatency
drwxr-xr-x 4 maas maas 4096 Sep 30 19:35 generic
drwxr-xr-x 3 maas maas 4096 Sep 30 19:35 hwe-16.04
drwxr-xr-x 3 maas maas 4096 Sep 30 19:35 hwe-16.04-lowlatency
drwxr-xr-x 3 maas maas 4096 Sep 30 19:35 hwe-16.10
drwxr-xr-x 3 maas maas 4096 Sep 30 19:36 hwe-16.10-lowlatency
drwxr-xr-x 4 maas maas 4096 Sep 30 19:35 hwe-p
drwxr-xr-x 4 maas maas 4096 Sep 30 19:35 hwe-q
drwxr-xr-x 4 maas maas 4096 Sep 30 19:35 hwe-r
drwxr-xr-x 4 maas maas 4096 Sep 30 19:35 hwe-s
drwxr-xr-x 4 maas maas 4096 Sep 30 19:35 hwe-t
drwxr-xr-x 4 maas maas 4096 Sep 30 19:35 hwe-u
drwxr-xr-x 4 maas maas 4096 Sep 30 19:35 hwe-v
drwxr-xr-x 4 maas maas 4096 Sep 30 19:35 hwe-w