Comment 1 for bug 1512219

Thanks for your bugreport.

I looked into this issue and it seems like its indeed a bug in apt that it will not properly do a version check when switching the candidate version to trusty-backports.

Attached is a patch that adds some debug code and also a potential fix for the problem, it breaks one of the existing tests, I need to inspect if the test is incorrect though. So its probably not the final diff but it highlights the prolem area.

For it to fully work you need to adjust the python3-lxc dependency in lxc too, please add something like:
  Depends: python3, python3-lxc (>= 1.1.4-0ubuntu1.1~ubuntu14.04.1)
(i.e. ensure that apt knows it needs to pick a reasonable high version). This is useful regardless of the diff.