Yeah, the pet thing happens. The pet tries to follow you, but it didn't enter right and was trying to pass through the walls on the sides and got stuck. Doesn't happen all the time, but it happens enough.
Enemies do the same, where they get stuck chasing someone or while doing their patrols, and get fused into a wall or even a rock on the ground, and because they go into combat mode when you attack them, but then they can't attack you, they reset their health and combat and become evade bugged. Notably, some won't evade bug because even though they're still stuck they can still attack you, for example, if you go into melee range or it's a caster that got stuck and you stay within range.
One place that's actually famous for evade monsters is the razorthorn trail (or whatever it's called) a bit to the northeast of Shattrah City, where there's a bunch of ravager monsters that are just stationarily evading anything.
It can actually be aggravating first few times you go there because there's a daily quest that involves killing the big patrolling monsters to try and get a low drop item that gives you a ravager pet (temporarily) so you can get quest items. When you get the item, you lob it at a ravager to tame it, but if you don't know about the stuck ravagers, chances are you'll lob it at one of the many stuck ravagers and lose the item, and have to start killing the big monsters all over again. Sooner or later you learn (the stuck ravagers actually tend to have a greyed out bar, as if someone else was already fighting them, although not always, and patrolling/moving ravagers are always unstuck) which to target, but I recall frustration first two times I did the daily quest.
And there's -tons- of bugs in WoW. I once jumped from the small cliff on horde side of WSG where the GY is just after rezzing, and instead of hitting the ground below, somehow I fell right -through- it, and kept falling into this blue empty space area, falling, falling, my dot getting farther and farther away from the battleground map just floating away helplessly. I had to wait until we won the BG before I got the option to leave BG and got unstuck. It was actually funny/neat though, not particularly annoying or anything.
And pets do funny things too. Did you know that once upon a time, when ZG first opened up, hunter and warlock pets were the reason that a plague spread through the server worlds, killing a vast community of players? Check it out:
http://en.wikipedia.org/wiki/Corrupted_Blood