Bugs that have been uncovered so far:
A duplicated number causing an error to popup when a baby spits up on you
Quantum cakes that exist only as long as you have no other cakes
A missing parenthesis allowing you to marry someone who should refuse you for being TOO SINFUL
The default name of the main character (Sorami) accidentally showing up in one of the ending stories even if you were using another name
Looking at your picture in the gallery after ending the game could sometimes throw you back into the gameworld after it ended... which, if you'd ended by turning 21, would then mean the game ended all over again
Popup error if you started to save the story-record available at the end of the game and then canceled
So far, nothing that actually crashes the game or really screws up progress.