There are other very serious bugs
It appears they have installed another layer in the file system starting around 10.10.
I have a FAT formated USB stick and from the command line this often happens:
$ cd /Volumes/RED8/
Opps all the files are gone except they aren't. Things like "ls -s | sort" won't work at all sometimes yet ls -s sometimes does. There are plenty of online complaints about this but most seem to think it is related to the shell which it isn't.
I don't know what that extra layer does but I expect it might help protect flash drives from being pulled out without being turned off first or related to their new file system but that is pure speculation. Maybe Apple should have used some of its huge pile of cash to by Larry a new boat and then roll out ZFS properly.