Neutered cat mounting?!?!

[arielb670]

My neutered male cat has a habbit of mounting my spayed female cat. I am not exactly sure why he does this. he was neutered at 6 months and was not introduced to my female cat until 2 month later (she was about 9 weeks old). At six months old I got her spayed. My male cat does this on a very regular basis (almost daily!). My question is could he have been neutered wrong? or is it possible that he is a criped orchid? I know a lot about horses and similar problems but i have never heard of a case with a cat like this. I know if a cat has been bred then neutered there is a possibility that they could act up when a female is in heat but my male was never around a female in heat when he was a baby. Does any one have any ideas on what the problem could be and if i could get it fix?

Thanks for your help!
~Ariel~