At the moment bzr treats deletion of a directory containing unversioned files (either ignored or unknown) as a conflict.
This is a bit annoying because often the unversioned files are generated trash, like .pyc files from Python. However in some cases people do have “precious” files that are ignored but shouldn’t be just deleted.
Vincent has a merge proposal up that will instead move the files into a bzr-orphans directory in the root of the tree.
What would you like to have happen? My feeling is that there should be a configuration option to choose the policy, and we should perhaps eventually distinguish “junk” (safe to delete) from “precious”, as Baz and GNU Arch did.