Alexandre Desbiens
Comments
From the Wiki:
Zombie Pigmen
-Now only drops gold nuggets and rare drops when killed by the player, either through combat or potions, or player-activated mechanisms such as manually lit TNT
-If killed without player intervention, only drops rotten flesh
It seems like an official change.
It seems to be normal, since Mushroom Soups cannot stack. If they are stacked by a command, then they are likely to behave strangely.