
The condition is called 'ovarian remnant syndrome'. In every case it is due to problem with the initial procedure carried out by the vet, a recent study has guggested that 17% of all bitches spayed have ORS, in a single dog household it may go undetected but with other dogs it can be a nightmare.
We had a lab speyed when she was 2 years old, a routine operation.
After 6 months she behaved exactly like an in season bitch would around dogs, tail to one side and peeing/marking everywhere, even her vulva was enlarged. We had 2 males labs at the time who followed her round, barking and whining all the time, but we put with it knowing that she could not possibly be 'in season'.
This behaviour was repeated every 3 months after, she was becoming intolerable, we had letters from the council about our dogs barking, whining and generally being a constant nuisance to our neighbours. Something was wrong but we didn't know what to do.
We eventually decided that our vet should examine her when she was next 'in season'. It turned out that that Alice did have something amiss and it was due to the spaying op. Apparently when a small amount amount of ovarian tissue is left in the abdomem it can attach itself to the body in Alices case to her kidney. The kidney then started emitting the hormone that triggers 'season' behaviour. The urine produced was full of hormone and attracted dogs, as does a normal in season bitch.
The vet gave 3 options for treatment
1, Do nothing - This was not a viable option
2, Repress through administering the anti season drug - This would have lasted for life requiring 4 treatments a year so that was not acceptable, Alice is now 13
3, Operate to find the ovarian tissue and remove it - That is what we opted for. It wasnt a routine operation as some abortive exploratory work had to be done, but Alice was completely cured. We were happy to get our Alice back to normal and she has lived happily every since.
I know this is an extreme example of the consequence of a routine operation going wrong, but does show that mistakes are made and that they can be diagnosed & corrected.