Fixed the same issue for me with CSSU/Stable (6.1). Also made it much faster than old Nokia PR1.3 so look forward to that if you upgrade! For some reason it was behaving as though it had the old notifier-id build-up bug from previous Nokia PR releases (though it didn't, no ids listed in that file); entering an inbox previously made it take up to a minute (usually 5-40seconds depending when was last refreshed/viewed/other unguessable factors) to show the list of emails, for ALL accounts (not just gmail, but that's my main account and it was worst affected). Hadn't reinstalled email accounts for a long time.

But upgrading to stable from PR1.3.1 also broke my (builtin) alarm sounds (I had profilesX installed before), theme desktop background, and my old sms/IM conversations disappeared - am gonna try to restore from the last backup for conversations - strongly recommend making backup before you do an upgrade! (though my n900 PR1.3 was a bit broken before, just not in those ways).