Periodically, when running together, he would trail off in a random direction, and clip through walls (while claiming to follow me). He was standing RIGHT there-- and I could bump into him and push him. Periodically he'd be attacked by zombies that were swinging at empty space while he axed them, and when he hit them, or when I killed a zombie, his position would suddenly update.
The screen shot below has me flipping him off -- as he stands right in the doorway for purposes of tracking. This is the long-barn/stables immediately next to the Berenzino construction site, although it happened all over.
We experienced almost no desync, and consistently had under 80 ping to the server, and very standard bandwidth. When visible, however, I was seeing him consistently rubber-banding, even though the player-list showed him and his ping and bandwidth as better then mine. {F30384}