test: known broken test for subject after reindexing

In [1], Mark gave a test that was behaving strangly. This turns out to
be specific to reindexing.  I suppose one could argue that picking the
lexicographically last file name is a defensible choice, but it's
almost as easy to take the first, which seems more intuitive. So mark
the current situation as broken.

[1]: id:1503859703-2973-1-git-send-email-markwalters1009@gmail.com