It was an effect of me changing the game to do all data displays via direct database queries. I had previously been storing a lot of player data in the session object (Which was being badly abused by Lander), but have changed to code to always update your database record immediately and to display all data based on your database record, versus the session variables.

The bank was properly updating your database record when depositing or withdrawing money, but was then trying to use the old session-based variables when displaying your new balance information, thus showing inaccurate data.