I had a warrior friend me afterwards and he said he couldn't attack with grommash. Maybe the patch broke something.
This bug has cropped up for me a couple times since the Warsong nerf patch. Charge minions get played onto the board and then you are unable to select them to attack. Cost me an arena game the first time it happened.
I read that it has to do with selecting them before their animation finishes? Not sure if that is true or not.