In order to fix this bug, it would seem so. On the Mercurial list, Adrian 
Buehlmann mentioned a similar Windows bug, filed as issue1713.

I don't know much about how fncache actually works, but it seems to me that it 
would be preferable to avoid ever creating files whose names begin with a dot 
or a space. While ‘.[^_]*’ should be safe, such files are normally hidden in 
shells, and that seems inappropriate for the store.