maas deletes products/images locally that do not exist remotely

Maas imports images to deploy and use for boot resources from streams. It imports a number of products from each stream, such as:
  com.ubuntu.maas.daily:v2:boot:14.04:amd64:hwe-t
  com.ubuntu.maas.daily:v2:boot:14.04:amd64:hwe-u
  com.ubuntu.maas.daily:v2:boot:14.04:amd64:hwe-v
  com.ubuntu.maas.daily:v2:boot:15.04:amd64:hwe-v

If the product is removed from the remote stream, and maas does 'boot resources import', it will be *deleted* locally. This is a bug for a few reasons:
 * accidental deletion of products on the server side will break customers.
 * Canonical cannot remove products *ever* from the server side
   if these products (such as 14.10) go unsupported, we'd like to no
   longer make them available or at very least move them to 'old-releases' like
   location. However, if we do that, then we'd be breaking existing
   users as they'd have workflow that worked before and not after.

I found this with the following.
Installed maas from maas-maintainers/stable.

$ dpkg-query --show maas
maas 1.8.2+bzr4041-0ubuntu1~trusty1

created a local mirror of stream data like:
$ sstream-mirror --max=1 --progress http://maas.ubuntu.com/images/ephemeral-v2/daily/streams/v1/index.json out.d os=ubuntu release=trusty arch=amd64

I then pointed maas at that mirror rather than the daily mirror.
I did the import, and dump-image-status (https://gist.github.com/smoser/2cec72d243404a72fdb5) which simply shows which products maas has available to deploy/use.

$ ./dump-image-status admin
ubuntu/trusty amd64/hwe-t 20151020 daily True
ubuntu/trusty amd64/hwe-u 20151020 daily True
ubuntu/trusty amd64/hwe-v 20151020 daily True

Then, I manually edited the stream data as seen: http://paste.ubuntu.com/12894365/
to remove the 'com.ubuntu.maas.daily:v2:boot:14.04:amd64:hwe-t' product.

And I re-imported:

$ maas admin boot-resources import

waited a bit, and saw:
$ ./dump-image-status admin
ubuntu/trusty amd64/hwe-u 20151020 daily True
ubuntu/trusty amd64/hwe-v 20151020 daily True