Many times my current pet changes to another random pet I have stabled. This usually happens when I log out while the pet is dismissed or while I am dead, or when I leave a battleground while I'm dead. Also, the stables interface is buggy and usually shows empty spots where stabled pets are supposed to be.
Yes but my problem is not that I'm "losing" pets, which is merely a cosmetic issue, but that I am forced to use "Call Stabled Pet" every now and then because my pet changes for a random one from my stable.