In multiplayer zombies can swim through cobblestone walls. Here you can see a YouTube video with a bug: http://www.youtube.com/watch?v=7JJdc82kuz4 or see atachment with the same file.
MC-11398
Cobblestone Wall Bug With Zombies
Resolved
Duplicate
0
Liudas
(Unassigned)
Unconfirmed
cobblestone, mob, multiplayer, walls, zombie
Minecraft 1.4.7
Retrieved
Duplicate of MC-10.