Update: Dead human bodies have this behavior as well. When someone is prone and alive, you can push their body in some cases by running into their feet.

Update: Appears to reproducible everywhere. Inside or outside does not matter. The area around the zombie feet blocks you. This could cause you to get stuck in a tight corridor.

The zombies bodies do not persist for a long time; but while they are there, you cannot walk over them. If you are in a corridor and you kill a zombie, you cannot walk past until the body is gone.