What I expected to happen: passive mobs will avoid lava. A hit mob will not jump to lava but it will flee in another direction.

What actually happened: passive mobs (pigs and sheep tested) do not avoid lava and fire caused by lava (burning trees, leaves, etc.). Instead, they can go onto the fire and die. Also when hit by the player, a mob can jump into the lava pit and burn out.

How to reproduce: find a lava lake and fire caused by it and observe the mobs. It should not be very hard as in snapshots of 1.7 lava pools are more likely to cause fire.

Note: this bug is similar to MC-721 (mobs do not flee when you lit fire on them). The difference is that they can also go into fire even without any player's actions.