Momento Mori on Ace of Spades is removed when scanning objects with your Ghost to gain progression in PvE activities (i.e. the beginning of the Arms Dealer strike). I know that in a previous weapon sandbox update Momento Mori was tuned so that it would be removed upon switching weapons, but the requirement of pulling out your ghost to scan to progress in an activity should not constitute switching of one's weapons. I know this is a small issue, but just thought that I'd pass it along to whomever deals with these small bugs.