I am reposting rabbitpams post here:
FROM RABBITPAM:
I sympathize with having the stones. Yes, he needs extra water daily.
BB, I had a really goofy idea so naturally I thought I’d post it publicly. Anyway, I was wondering if the issue isn’t so much Jack having something that makes him hump Vivian more than ever, but whether it’s Vivian who is stimulating him more? What if Vivian has a hormone imbalance that makes her give off the scent that says she’s in heat? Like it’s stuck in the ON position or something. If she has high hormone levels despite being spayed, that could add to her aggressive behavior at the shelter, and maybe she just smells delicious to Jack. Was she ever tested?
Anyway, we know that it takes a month post-spay for the girls to calm down, so maybe Jack’s innards need to settle over a couple of weeks to relax now that the stone is gone. Hang in there.
MY RESPONSE:
I don’t think that is goofy at all. The vet actually mentioned that maybe it was Vivian – a UTI or something. So we actually have an appointment for her too. So we’ll see! He definitely finds her delicious! I mean part of it is dominance, but he does more honking and “mating” ritual behavior before he tries to mount, more than he does the dominance mounting behavior.
And though Vivian may have been aggressive at the shelter (territorial with her cage). She is not like that at all here. She is very sweet. She will try and bite or scratch only when she thinks you are trying to pick her up, but other than that, she doesn’t show any territorial aggression or anything. (Nothing like Rucy used to do in her younger days). Vivian is really such a smart, funny and very sweet bunny.
And the other thing that really brings me back to thinking it’s just him is that during dating he went bonker trying to mate every single date. One we barely got in the pen before he humped her. She got in and before she could even figure out where she was he mounted her.(but again, it was the beginning of Spring – so….so many different factors it’s hard to narrow!) It was only Vivian that didn’t end up fighting with him about it. She does need to though, he doesn’t get aggressive with her so far when she does speak her mind, but she doesn’t do it very often. So, I don’t know. Vivian is so sweet and nice to him even when he’s rude.
I don’t know – I’m just thinking myself into circles- so many different factors to consider. We’ll just try and conquer them one at a time I guess.
First factor – WHEN IS SPRING OFFICIALLY OVER?!!
(and do bunnies have this marked on their calendars?!) 
I have never felt so baffled before which is why I decided to just to post about it.. This is definitely a problem that I haven’t figured out yet. And hopefully if I solve this problem – then, it will help someone else dealing with something similar.