I thought it might have been due to a hack so I removed all my hacks and it still happened. Then, I removed my whole downloads folder and... it still happened. Must be a Maxis thing. Hope they fix it. It wasn't happening to me until I installed seasons though. There must be a conflict with seasons and pets or something. Hopefully they can fix it with a patch or something. It's like the infamous jump bug all over again, but with pets.