When another player kills the player, the player that died will poise as if it is drawing a bow. If the player poising like drawing a bow and kills another player, the player's poise will fix, but another player will poise like drawing a bow. It won't happen when other mobs killed the player. It happened when playing in LAN. Both the players could see the poise. Both players should be in survival mode. If one of them change into creative mode, the poise will fix. If the player that killed the player die, the player that has the poise will fix.