Male dog acting like spayed female is in heat

[Liquorish]

Since his sister was spayed 2 years ago, every couple of months my dog becomes absolutely possessed as if she’s still going into heat. No other male dog acts like this when around her or even sniffs her. The only thing to do is keep them separated until the phantom heat is over. Anyone else experienced something like this and have any idea what causes it?

I wonder if there's still a bit of reproductive tissue or something that was left behind when she was spayed so her smell changes when she should come into heat and obviously your dog notices more because he lives with her?

I actually watched a vet program the other day (Dr Jeff) where a bitch had been "spayed" but she was still coming into season because a bit of her ovary had been left behind. Dr Jeff had to go in and look for it and fish it out, he said that even a small bit of reproductive tissue left behind can cause hormones to change and even make them come into season in some cases which I never knew.

I’ve wondered that too, my bitch is spayed and a couple of times a year she smells different and we get attention from male dogs.