Well that's what it looks like! Stan (male, neutered) and Bunty (female, neutered) have this routine where Bunty rolls on her back near Stan and waves her paws around suggestively. He then jumps on her - they roll about grunting, then one of them will start licking and grooming the other one's head and ears. Bunty then rolls to one side, flapping her paw about before standing up, waggling her bottom and taking a flying leap onto Stan again.
This rolling about and grooming continues till one gets bored and wanders off, or one goes a bit too far and yelps before running off.
All very un-neutered behaviour!
Can anyone shed any light?