When you have the left mouse button held down while moving through an archway. Keeping it pressed then pull your inquisitor back through the archway back around the wall, and then press and hold space bar to move him/her into cover he does a looped running animation until you release any of the aforementioned buttons.
Like i said a very tiny animation error but that is what bug reports are for right ? =)
"Venerate the Immortal Emperor"