I took Tonks to the vet because she has what I call wet butt. (No poop just wet). I thought maybe she had a UTI or something like someone suggested.  She has NO other symptoms though. She has been pooping a little bit outside he litter box but when she’s out and about she is not dropping any poops on the floor. She is also not peeing anywhere but her litter box. She gets this whole wet butt things about every 4 to 5 months and wants to hump my cat some. Before I have my wonderful vet that I have now the previous place I took her to said there was nothing I could do except give her a butt bath with medicated shampoo.  Well it turns out she does not have a UTI and the vet said if he knew she was not spayed he would think she was in heat. He said this sounds totally hormonal and that there is a big possibility that when she was spayed at the humane society that they may of left part of her ovary or some tissue behind. He said for now to monitor and keep a log of when she does this. I have to up her butt bath time to everyday with the medicated shampoo and he gave me some ointment to put on the raw spots.  If it gets much worse he said we may do and xray of her insides kidneys etc… to see if there is something weird there. He said he has never really seen anything exactly like this (and he sees alot of rabbits) so he is going to do some research on hormone therapies.  Anyway sorry this was so long just wanted to give you and update or reference in case this happens to your bunny!!!