Back when I had Buddy and he was bonded with Carmel, he mounted her everyday. They were both fixed and hormones had long since dissipated, but he would still be on her.
They could be laying across the room from each other and Buddy would suddenly sit up, thump, and race over to Carmel to start humping. It could be her head, or her butt, it didn't matter to him. Sometimes she would get up and hop away, sometimes she would just sit there til he was done, and sometimes I would push him off her and tell him NO!
I asked my vet about it and she said that Carmel may have been oblivious to the fact that Buddy thought he was the dominant bun. She may have not been obeying the bunny hierarchy that Buddy was demanding. So he felt that he had to continuously remind her. But he didn't ever really bite her or anything...other than the endless mounting, they were very bonded.
It really was apitiful sight though. Carmel was so large and Buddy was tiny. He'd have to latch onto the fur on her hind end with his teeth just to hold on. And even then he would fall off midway thru.
One time, he mounted her head and really got on her to where her head was poking out thru his back legs. Then Carmel decided to get up and run, so Buddy was holding on for dear life, facing backward, piggy back on Carmel while she ran the length of the living room--crazy and an absolutely hilarious sight!:tongue
-Beth