IMAP Settings keep reverting back to default...

I've been using IMAP in Mail to sync with my Gmail account, and I recently started having connection problems with the server error saying something like: "too many simultaneous connections". I had configured all the settings under Account Info in Mail per Gmail's instructions (i.e. don't store sent messages on server, etc.), but I noticed a problem: those settings that I choose are not retained when I quit the program! All the boxes in Mailbox Behaviors that I had unticked per Gmail's instructions are RE-ticked when I reopen the program after a quit or shutdown.

This is extremely frustrating. Can anyone offer any help on this?