As I'm training my 3rd generation Nightmare (69) - he got great talents each at teen and adult. But when he hit ancient, he got 2 piercemonger - occupying 2 slots with 2 cards. So it says he has 4/4 talents.
Will I get another talent if I get him epic? I am still looking for spritely to come in...
It is probably due to the genetic matings you have carried out. The offspring got the talent twice, and it doesn't know not to give you it twice. My guess is that if you take it up to get the 4th talent, you might get a fifth...if not, that is the time to contact support.
Not a mistake, or a cheat, simply a gift from KI for being such a dedicated pet breeder.