The bug

If you hit a mob with a snowball and then that mob dies of other causes (for example magma blocks, cacti, or fire), that death is not counted as a player kill. Therefore, the mob does neither drop its armor and gear, nor any experience points.

To reproduce

1. Run

   /summon husk ~ ~ ~ {ArmorDropChances:[0.0f,0.0f,0.0f,1.0f],ArmorItems:[{},{},{},{id:"minecraft:iron_helmet",Count:1b}],HandDropChances:[1.0f,0.0f],HandItems:[{id:"minecraft:iron_sword",Count:1b},{}]}

2. Kill the husk with a sword
3. The husk always drops its helmet and sword
4. Run that command again
5. Hit the mob with a snowball
6. Kill the husk with /kill, or let it die on magma blocks, through fire, or through other means
7. The husk won't drop its gear, and no experience points

Original description

When a player does damage to a mob and it dies shortly after it would drop its loot. This is currently broken now (probably broken when they fixed the dog player-loot tables).

What use to happen:
Player hits zombie with snow ball
zombie dies on magma block shortly after
zombie drop xp, main loot, and chance of gear/tools it was holding

What does happen:
Player hits zombie with snow ball
zombie dies on magma block shortly after
zombie drop xp, main loot, and NEVER drops gear/tools