Invincible sleepers/inviseable creepers

I’ve encountered this a couple times on the Official Seattle server, pretty sure its an exploit that has to do with them loging out, changing a client-side file or directory, then logging back in to ghost around or something… the last time i was killed/blindsided when i first found the sleeper, which seemed weird because i was being very watchful in a wide-open dessert… I returned and put another 5 arrows in him then hid and watched, after another minute I heard gunshots near the body but didn’t see anybody to be firing them…

I don’t normally record but i may try just to capture this for ya. I’ll wait till i have video evidence before namedropping.