This happened over the last few hours of us playing on a server, and I don't remember 100% what exactly it was, but either
a) When a remnant possesses an entity, his blue vignette effect jumps to another player
or
b) When a remnant possessing an entity regains his human form, his blue vignette effect jumps to another player

Sorry that it's kinda vague but thats about all the info i have, but i'll keep a closer eye on it shortly