So I recently started with this all Pet Battle thing, especially because I love pets and achievements and I wanted to farm these two.
I end up choosing Celestial Dragon as main pet for leveling, and will level Disgusting Oozeling and Magical Crawdad with the dragon aswell.
Anyway, I was leveling my pet, catching other pets for the 250 pets achievement when suddently, I level up to level 6, get out of the pet battle, and I was still level 5. I did two more battles and leveled up to 6 in both and still was level 5 after leaving the battle.
Then I went to STV and tried to catch a pet (Polly) and after sucessfully catching it, I got out of the battle, and didn't got the pet. I didn't got the pet in the journal, I didn't got the experience on the Celestial Dragon, and it also didn't count for the "Master Pet Battler". It did however count to "Local Pet Mauler" (Stranglethorn was the place) and I got the achievement because it was the 10th area I was fighting on.
So, wtf? I have some screenshots here:
This one you can see that I won 180 exp on my Celestial Dragon, but still after the fight I'm at 44/450.
And in this one, althought in the chat I leved 3 times to level 6 with my Celestial Dragon, I'm still level 5!
So... wtf? xD
To me it only got fixed when I exitted wow and reopened.