Mobs of any kind have problems moving on Snow layers, making it possible to approach certain mobs that you would normally not be able to approach, with this bug I have been able to stand next to an Enderman and look him straight in the eye without him being able to attack me.

How to recreate: Journey to a Snow biome, wait for serveral weather cycles and Snow falls, then note how mobs become imobile or even float above invisible Snow Layers, have for instance a Creeper chase you, note that after a short while it will become stuck and unable to move.

Hopefully this is worded correctly and cannot in any way be misconstrued.