I noticed many times I enter the bg, the character stucks at a friendly player trying to attack him. It doesn't matter if the target is horde or alliance, what is wrong is that it shouldnt attack target of the same battleground faction. Noticed this only on blaackrock (AT), where bg are cross-faction.
Now for example it just joined an eye of the storm battle and it is trying to attack another alliance player (same faction, same bg faction, but we are both playing as HORDE side)
I don't know how it happens and why but it looks pretty bottish.