I can't get content referenced in a dead repo to be considered unused.

Setup:

1. Make repo A and B, connect them
2. Add file to A, copy to B, sync
3. Sync B
4. Mark A dead
5. Delete symlink from B
6. Run git-annex forget --drop-dead on B
7. Run git-annex unused on B

The file does not appear as unused. Am I doing something wrong or is this genuinely impossible?

I can understand the reasons for not wanting it to work this way in case the dead repo had important files, but what this means is files I genuinely want to drop will never be considered unused if they existed in the dead repo. This could create an issue for me if I lose a repo in one of my very large annexes, because that could mean gigs of wasted space. I rely on unused to safely drop content because the drop command may remove files that are still referenced somewhere else (duplicate symlinks).
