[eider]

Quote:

In the past, AFK players were only invincible because clients reported when they took damage (rather than when they gave damage)

It's not 100% like you said, but in very big brief - yes.

Quote:

The new sync probably fixed this accidentally, and it might have been reverted to maintain the behaviour of the past 7 years on this issue. Just my hypothesis, anyway!

I don't think player's invincible in AFK was a bug, rather intentional behavior. Anyways, 0.3z changed this in some parts. AFK player can now be killed but NOT when he's AFK. Damage is processed (HP loos and eventually death) right after exiting from AFK, and it will work only if attacker is still streamed and is not AFK.