Started like this:
I logged in at NWAF in a tent, ran out to start my looting cycle of the tents.
Then i heard a zombie, looked around and saw nothing. Then it started hitting me while i was trying to escpare. I was healthy and it killed my with 3-4 punches (i was standing up).
So i was basiclly killed by an invisible zombie in just a few seconds.
This was on stable branch.