Hmm, our Bungle used to chase the cats all over the place, they were so patient with him most of the time and just kept running away.
The thing is that its not all about sex, he is trying to communicate with them and establish himself as the dominant one. It used to break my heart when I saw Bungle sticking his head out to be groomed and them ignoring him.
Has he got a bunny friend? If not, perhaps thats the answer, our buns who live in the house with our 2 cats dont bother the cats really and the cats are just about used to them now too.