I want to say this started with the April patch but not entirely sure. There will occasionally be a floating bag - the small pouch you normally see when you drop something on the ground - centered on a mob for a few seconds. If I had to guess, it is the spell particle effect for -- well I don't know what -- that is showing as a bag instead of whatever glittery sparkles it is supposed to be. I don't think it is a beastlord spell though since I only see it in raids (I play a BL). It exists, sorry I can't pinpoint it though.