Mobs apparently don't give any EXP orb when falling from a really high place and die. I was playing with a friend of mine on a server testing out the new snapshot and we discovered that the mobs falling down from our mob grinder weren't giving any EXP orb on dying, i am not sure if it is a bug or just a new feature.

P.S: They were giving EXP if killed by hand or any weapon.