I have 2 cats (brother/sister littermates) just gone 5 years old. They were neutered/spayed at 6months old. The female pretends to spray, usually me or the occassional visitor. Typically if I go to the bathroom she will follow me, open the door and come in, then she'll turn her back to me and vibe her tail/bum at my legs. Touch wood she hasn't actually sprayed but the behaviour is a little disconcerting. It's not sudden new behaviour but something she is starting to increase doing.