so, id taken a bunch of pills, then drank a keg of soda. normal bloating reaction. after that, i realised that the belly rub station can give money, so i sat there for a while, and that caused the stomach capacity to hit negative numbers.
i havent been able to recreate the bug, but i did manage to fix it by entering an eating contest, although i cant confirm if that was a fix for the negative capacity, or the permanent bloating, as i cant recreate