Several Hunter players are reporting issues with their new pet enhancement in Patch 2.3. as well as strange pet behavior and pathing. Biljre (from Blizzard) confirmed this issue is being investigated. If you have had this problems or new ones make sure to report your incidents over at the following forum thread. Read what others are reporting.
Bunter @ Perenolde: “I noticed several bugs in Karazhan last night in regards to my hunter pet. When we were on the stairs leading to Moroes my pet decided to go to the Spider/Bat/Hound area of the instance (right under the steps) when I had him attack a non-elite mob tied to Moroes. This behavior happened for the other hunter in the raid group. Because of this problem it lead to two wipes for the raid group because they aggroed many spiders from that area.
Also, when we were in the hallway leading to Maiden my pet would not attack when the mob had its back to the wall. When I had the tank move the mob away from the wall, then my pet went in to attack.
Both of these bugs seem to be related to the new pet feature that will have them attack the mob from behind, but as you can see in these situations it is quite buggy.”