Getting hit while on fire and blocking causes reverse knock back

[staridiot]

Expected behavior

You just shouldn't take knock back (or in this case, knock forward) when blocking (with some exceptions, like the hoglin), regardless of status effects or if you're on fire.

Observed/Actual behavior

If you use a shield to block and get hit by a zombie which has a weapon of fire aspect, it will cause you to be thrown into the zombie. This also happens with status effects such as poison and wither, if you take damage on the same tick as you're hit by a mob, it'll throw you up and towards the mob. The first example, for some reason doesn't work on vanilla, but does on Spigot and Paper.

Do note, the getting set on fire by a zombie even though you're blocking is probably a bug, but its not the one I'm attempting to report.

I put together a quick video here demonstrating the issue.

Steps/models to reproduce

Get a shield, summon a zombie with a fire aspect weapon. Run either spigot or paper (this specific example doesn't seem to work on vanilla). Block with the shield and get hit by the zombie, the damage from the fire sudden has a boat load of knock back which sends you up and into the zombie.

Plugin and Datapack List

None
None

Paper version

This server is running Paper version git-Paper-237 (MC: 1.18.2) (Implementing API version 1.18.2-R0.1-SNAPSHOT) (Git: b55ba19)

Other

Also tried with vanilla Minecraft 1.18.2 downloaded 3/10/22
And Spigot; This server is running CraftBukkit version 3453-Spigot-ffcceeae-64db512 (MC 1.18.2) (Implementing API version 1.18.2-R0.1-SNAPSHOT)
The video I made demonstrating this issue: https://www.youtube.com/watch?v=JspnG8fyKEU

[Lulu13022002]

This is related to https://bugs.mojang.com/browse/MC-147694 but is only visible on spigot due to heavily changed damage logic (the DamageModifier API, and stuff around). In short vanilla always knockback the defender instead of the attacker but it's not noticeable in vanilla since the defender gets also knocked in the opposed direction and the hurtMarked is false anyway.
This logic however doesn't happen on spigot cause the damageEntity0 return false in this case and so the last knockback is not dealt. The reason this only happens later with another damage is that the hurtMarked boolean is not updated before.
Fixing the underlying vanilla bug will fix this issue however i would prefer remaking the way the damage are handled