Stunned at start of battle

I'll sometimes get a message at the beginning of a battle saying I cannot do that while stun. I'm level 4 fighting mobs below my level on traveler's way. I enter battle and hit auto attack and recieve that message. I usually get the message if I hit autoattack before being struck by the mobs. It's weird that it doesn't happen every time either.

[Glitchless]

That will be fixed with the next patch unless you are encumbered in which case it will now be a stun effect that prevents you from doing actions when entering combat for a short while to prevent people from using their sleight of hand gems.