[[!comment format=mdwn
 username="joey"
 subject="""comment 3"""
 date="2015-10-06T21:10:44Z"
 content="""
Intriguingly, debugging shows it's checking the preferred content of
the repo it's in, rather than of the repo it's copying to!

And indeed, git-annex sync --content doesn't copy the file to B.
So, this bug is in `git-annex copy --to --auto`, and not in preferred
content handling in general.
"""]]