I saw a post on this topic but it was not answered.
I have a Parallels shared folder (a OSX folder that I access in Parallels) however the folder keeps getting hidden in OSX. I can see it in Windows (Parallels) but not in OSX.
I have run into the same problem. Something appears to have damaged the OSX partition structure. After restoring from backup I can see the shared folder in the Finder but the Apple backup program will no longer back up the partition the shared folder is in. It's message states that there is nothing to back up. All of this workded up until a few days ago after installing the 5160 update.
The problem started with 5160. In another forum topic several people have reported the same problem. I do not have any software to fix the problem. Called Apple Care and they did not have any suggestion -- they didn't have anything in their database that would help.