Cannot add permissions to a file share in File Sharing Preferences
The hard drive I installed the fresh copy of OS X 10.9.4 completely died last week. I suspect that this hard drive failure was unrelated to the issues, but when I re-installed OS X again and went to add the share drives, everything worked as normal.

I suspect that this is an obscure bug, but if you come across this issue, a reinstall may fix it, as this worked for me.