If it appears that the animations are not playing when you are using the keystroke attacks in mouselook. (holding the left mouse key down and tapping the keyboard arrow keys) Please make sure you are using the latest HUD update.

To check for updates go to the options menu on your HUD, and select the update button.

I changed the update system a while back, so if you are using an older HUD you may need to update a couple of times.