When my hunter logs into cata I find my pet’s talents have reset to zero. This is annoying. Is it a known bug?
Is this your first time logging on your hunter in Cata? If so, it’s because the pet talents have been changed.
For me it started happening at some point during the leveling process and then it happened every time I dinged. Now that my hunter is 85 my pet talents have not reset on their own
No, I’ve leveled this hunter from 1 to 77 in Cata. It’s only just started happening, I can spend my pet’s talent points, save, log out then back in again and my pet;s talents have been reset to zero.
That’s an annoying bug I haven’t encountered (luckily) yet. My active pet had a tendency to reset when I dinged between 80-85, and then again when I changed specs. 
Our hunter met bug/problem with his pet doing barely any dps from auto attacks. Turned oud he had “old world” pre shattering catched wolf. This problems eroded when he sayed goodbye to his old champ and caught a new pet from current world content. Maybe that would help with your talent situation as well. Get a new pet.
Did he try to stable it first and take out?
I think he did, it didn’t helped, he put it into stable for keep sake and got a new one.