false heat

Hope someone can help me with this.
I have a female cat, Little Mo, that is exhibiting every sign of heat. However, this is impossible, as the vet has done an exploratory surgery to make sure no ovarian tissue was left inside when she was spayed.
This false heat occurs about every two months for a week.
Has anybody had any experience with this. My vet does not know what could be causing this which leaves me feeling somewhat helpless. I live in Florida, so my cats are able to be on the lani quite a lot, and Little Mo's verbal communications are reaching some tomcats (another story) who are having rather frequent altercations.
Thanks for listening
Miss Oreo

I am no expert by no means. But I have a 7 month old male that has been fixed and he still tries to "get it on" with a certain cashmere throw I have. Maybe they still have urges not sure.

But that is all you need a bunch of Tom Cats moaning outside your house! lol

evan a fixed animal can still "do it" .. they just cant cause any little suprises

MadSugar and Sharky,
Thanks for your responses. The worst part almost is that my other cat, Cosmo, doesn't understand why his sister won't play with him when she's in this "mood."
MadSugar,
How does your chasmier throw handle the "advances" of your male. Maybe it takes several months for cats to adjust to their new state of sterility.
Well, anyway, thanks to your both.
carlie