mob kills due to knock back from a sweep attack fail to reward EXP

Expectation: Knocking a group of skeletons into lava using the sweep attack should reward EXP for the entire group.

Result: EXP was rewarded only for the skeleton directly hit (I.E. damaged) by the sword.

To Reproduce: Gather a group of skeletons in a 1x1 hole with lava suspended above their heads. Using a sweep attack on the skeletons will knock them all into the lava, killing them, but only reward EXP for the skeleton damaged by the attack.