Look at the top left corner of this screenshot.
These shown nametags will just sit there in the corner for the rest of a playing session, and more nametags will accumulate the longer you keep moving to different maps in a Zombie Massacre session. Only by just completely starting a new game will the nametags go away. The more players you’re playing with, the more nametags that will get piled there.
Bad things probably will happen if someone had a particularly long play session with a bunch of players, cycling through various maps.
Steps to Reproduce
Play with friends or randoms in Zombie Massacre. Finish a map. Load any new map.