Creatures with defender killed in combat last turn

Delnai

As it stands right now, creatures with defender that take lethal damage on the same turn that the player takes lethal damage don't die. This is confusing; I get that creatures don't die to combat damage until all damage has been assigned, but why should a planeswalker that takes lethal damage after a creature die before that creature? That just seems wrong. The planeswalker and the creature should both die, at the same time, at the end of combat.

Obviously this is a small issue, mostly just occasionally affecting "Kill X or more/less creatures" bonus objectives. It may not even properly be a bug. But it's definitely unintuitive.