During earlier versions of Minecraft monsters could track the player through blocks. When a one-wide wall of transparent blocks [glass/iron bars/stained glass/glass panes/vines/fences] is located between myself and a hostile mob in 14w30c, the mob ignores me completely [in survival], even if all it has to do is walk two blocks around the wall in order to find me.
On the other hand, if I make a mob aware of my presence in survival [punching it, jumping so my head is visible over the transparent wall], it will lock on to my position and will quite happily pathfind through a maze of opaque blocks in order to find me. Zombies can locate villagers through any opaque or transparent block, but fail to do the same with the player.
This ability for any aggro hostile mob to track a player despite blocks impeding line-of-sight is inconsistent with the mob not being aware of the player's presense through those same blocks when not aggro.