While playing on my server I had noticed cows roaming about after I had accidentally done the /kill @e. The only cows that should be alive were the ones we spawned in. After watching them for a while I saw one walk right through the block like it was air.
Environment
OpenSuse Linux 13.1(Running server on own computer and playing at same time) Java build 1.7.0_59
Steps to reproduce:
1.Get a fenced in area
2.Spawn animals into area,
3.Wait