male cat humping

My male cat Da-Ku has begun attempting to mount/hump my female cat Pwne. He is 1.5 yrs old and neutered and she is 3 yrs old and spayed. Never did this before at all. I was gone for a week in Arizona and when I returned, he has been doing this. He doesn't get to the humping action really just gets into position. She just wiggles or rolls out of his reach and hisses. Then they are okay. He will watch her for awhile and then go on his way. He has done it about 3 seperate times today that I have witnessed. Any thoughts? He only does this to her and there are 3 other females in the house (all spayed). I am assuming it's an alpha cat thing. But she has always been it and he is a wimpy baby cat. He is very submissive normally.

I agree that is probably dominance behavior, but even neutered males will "do the deed" sometimes and even spayed females can be willing partners.

it's a freudian thing! yr male cat sees the older female as his mother and he's in LOVE!

my male cat, nicky, is almost a year, and he's been neutered for a while now, and i still occasionally catch him humping water bottles.
it's strange.