Originally Posted by BillSeurer 
Another example of this is the "killing blow" maneuver. It sometimes takes 4 or 5 tries before you actually finish off the foe instead of sheathing your weapon.
Either your timing is wrong and you make a different move, or two moves/options are combined to one key. I don't sheath my weapon with LMB nor RMB, so how can I sheath my weapon with a combination of LMB and RMB.