Renaming shared mailbox makes it disappear from sharee

I've run into an interesting thing.  If a mailbox has been shared to a second user (I'll call it the sharee), and there are subfolders on that mailbox, and the sharee renames one of those subfolders, it disappears from view to the sharee.  The only way I've been able discover to fix it is to hav

Best practices for mailbox network file storage?

Is there a current best practice for a shared filesystem backend for mailboxes (in my case, all virtual accounts)?  NFS 3/4, GFS2, GlusterFS, other?  In the case of the latter ones, is the use of Director necessary?  Any specific anti-recommendations?  Also, if it matters, I *think* I want to us