I am currently in the process of bonding my two bunnies Pixel (spayed female, rex, 2 years old) and Patches (nutered male, lop, 2 years old). I am currently in the 3 month of bonding and seem to be stuck! Patches 'chose' Pixel from a local shelter and things were going wonderfully when we brought her home.

Lately I have been attempting to introduce them in neutral territory, and the same behavior keeps happening. No mounting has occured, and the male consistently demands grooming by placing his head on the ground for the female. She always seems to attempt to force her head under his, fails, and then proceeds to 'nip-groom' him. I have tried to amend this behavior by using peanut butter to try to teach proper grooming and by 'disciplining' her when she does nip around his face. He obviously gets very agitated, and I am at a loss as to what to do! 

There have been no serious fights, and when placed next to eachother in different cages, they prefer to be next to eachother. It just seems that once they are together, they can't work things out!

I am wondering if I should just let her nip-groom him and let them work it out, if they are just going through a phase, or if they are simply not compatiable like I originally believed. 

Do they fight when they are together or just ask for grooms? If they aren't fighting that is good.

Grooming may come much later - I say as long as they tolerate each other don't force the grooming. Not all pairs groom each other - some are content to just sit by the other mate or lounge around them.

Welcome here. It does sound like they are getting along okay. Some rabbits are not too great at grooming initially, so like Sarita said, just give them time to work that out.

I would not use peanut butter to entice grooming. That's going to be too high in fat (and maybe sugar?) and rabbits shouldn't have any nuts, seeds, cereal pieces, or corn. You can try some mashed banana, just a little bit.