On Sunday the 27.11.2016 I logged into an experimental server after another experimental server crashed within 30 seconds after I joined.
I was able to move around my character freely - and at first glance everything seemed to be normal for me. But in fact, I was completely invisible for other players. Meaning, that I could see (their character) and hear (steps) them and also damage them with fists, but they could not! Also I could not pickup or use any items (open doors,...), but I could drop items. The dropped items would spawn where I originally spawned in. Being close to my spawn point I could pick up those items again.
Whenever friends where right next to my spawn, they could check my pulse and also interact with my still invisible body.
In the closer range around my original spawn I could also hit and kill zombies, although they did not fight against me. When I left to see how far I can run with that bug, I experienced some other important aspects. First: I could not anymore see and hear other players anymore. Secondly: I could not see a helicopter crash-site others could see.
If I would have wanted to abuse this bug, I would only be able to scout (and damage players) around the closer (<1000m radius) area next to where my character originally spawned in.