[Torquemadaa]

Having the same problem, but using Bartender4's bag interface. Since it appears to be happening to any addon that has "bag" calls, my guess woudl be it's a change in the WoW code, requiring addon authors to do a patch 4.1 update. Unlike some posts, my bags work (since Bartender4 simply calls the WoW bags) .... it's just that they ALL open anytime I go to a mailbox, banker or vendor, as though I'm pressing alt-B; and when I leave the banker/vendor/mailbox, they all close including any that I manually opened beforehand.