I feel silly because I didn't take an error log, but I figure I'll at least see if this has happened to anybody else.
I was playing a lot with two dogs and their three puppies. This lot also has a woman and her child, and the DMA Bordello set. I would first assume the problem is either Maxian or Non-Awesome, naturally.
I decided to donate three of the puppies to the adoption pool. I did so, the police came and took the puppies away. I was playing with the family and the Bordello set, making some money, and had the two adult dogs go try for some more pups. While this was happening, all the visitors to the Bordello finally noticed the puppy and started playing around with him. Eventually one of the DMA NPCs picked him up, and then he was stuck in the NPC's hands. The NPC took a bath with the puppy in his hands and walked around with him for a while, but I hoped maybe he would put him down eventually. He didn't, of course, and then he went to change the channel on the television and the puppy turned into a remote control
and disappeared from the household list.
Since it happened with a custom NPC I definitely assume it was that, so really unless anyone else has any ideas for what it would have been, I can only use this thread as a suggestion to not use any such sets with puppies or kittens on the lot. If this happens again, I will definitely record the error log here. b