Mobs killed in creative mode don't drop experience

The original bug I submitted pertained to animals not spawned with an egg. These are my farm animals that were bred naturally and they are not dropping XP.

I believe the issue is that the killed_by_player condition is not being applied/met when killing an entity in creative mode. With 1.16.pre2 I used a data pack to add two drop items to a mob, both with 100% chance but the second item has a killed_by_player condition. Spawned the mob from an egg twice. Killed the first mob with a sword while in creative mode, then switched to survival mode and killed the second one. They both dropped the first item, but only the second mob, killed while in survival mode, dropped the second item with the killed_by_player condition.

I'm experiencing a similar issue, but somehow the way I'm seeing it is different.

For starters, ALL mobs I've killed dropped items. The ones I've killed that didn't drop any experience is because I was either in Creative Mode and/or I killed them with a way that does not involve the killed_by_player condition (which includes melee attacks, bows, potions, etc.). Killing a mob without that condition would be something like pouring lava, lighting them on fire (with a flint and steel), and other things that would not make a neutral mob upset. Also, based on my experience, this is happening with all mobs: ones spawned naturally, ones from spawn eggs, and ones from /summon.

Same cause as MC-187504