Brittanybunnyjones, I would like to share my recent experience. Although it might be more info than the answer you were looking for, but you might see bunnies humping even after successful bonding and hope my story will give you some hope
I live in Australia and it started to get warm about 2 months ago in my state. This is the first spring since we had two bunnies – we had our boy bun 18 months ago and our new girl 6 months ago. Both bunnies were desexed as soon as it was possible for them and their hormone were settled down when they were first introduced. In spring last year our boy was the only bun in the house, spring caused nothing special in his behaviour. When the girl bun arrived in autumn, he did some territorial chasing and humping, but after 3 days of bonding they became best friends and we could only see grooming and snuggling. He’s more the boss bunny but would still groom her a bit… Until this spring! The boy started to sniffing the girl’s bottom a lot and trying to hump her tirelessly! sometimes it’s very forced, but sometimes he would groom her so much then chinned her body then start the humping. His legs are too short for her (they’re similar size but she has high arch), so he always have to grab her fur with his teeth to keep on top of her. Sometimes he would bite her back and bottom a bit, occasionally he would dig her. Our girl is such a innocent sweetie she didn’t seem to know what’s happening to her. I don’t think she would ever enjoy sex like human do, but I don’t think the sex itself bothers her much either, it’s more the fur pulling and biting that annoys her. she tolerated him mostly then run away. My heart broke every day to see chunks of hair in the cage and I tried my best to separate them whenever I saw the humping in action. Sometimes I picked him up when he humped, I could hear him breathing super heavy and his ears were very hot. I bought a similar sized stuffed toy and rubbed her smell on it hoping he could use that as a placebo but he just threw the toy away like he was jealous. He never humps our legs or anything else either, he was only interested in the girl
she wasn’t stressed because very soon she would jump onto his floor again and try to snuggle; seemed like she found a couple of ‘safe places’ where he can’t get to her so seemed like they found a way to make their dynamic work. But I still planned on taking them to the vet as soon as I see any distress
My fiance moved the bunny cage to his study and told me his observation. He said if he just sat there doing his own things on his computer, making not much noise or show no obvious tendency to go near the cage, the bunnies will act like usual, eating, sleeping, snuggling and grooming, but whenever my fiance needed to get up, as soon as he walked towards the cage, our boy bun will start the humping. So again, it’s almost like jealousy, like it’s a competition, that our boy thinks the human and the toy are competitors, that we might try to mate with his girlfriend?? So he had to have her before everyone else get to him?
I got the conclusion, in our case the cause of the humping is a mixture:
– there’s the physical factor: his hormone or sexual drive is a bit more active, maybe she was releasing some scent as well in spring
– then there’s the behavioral factor: he think she’s his and only his, he gets aggressive when competitors were present; and on the other hand, he still loves us human, he knows we’re the food/pat providers, his attention craving made him excited that also triggers the humping
In the end, I like to give you the good news,his humping stopped just 2 days ago. when it’s treats time or free roaming time, he seemed is purely excited about the freedom or yummy food again. It was such a relief. What’s more, in average he’s grooming her a lot more.
I hope it won’t happen next year that they’re both older, but if it happens again I will know it won’t last forever