Mobs don't take knockback if hit after taking lesser damage which doesn't deal knockback

I was playing in a normal Minecraft world, I hit a villager, after burning him with a lighter.

*What I expected to happen was:
That the villager took knockback.

What actually happened was...:
When I hit him, he just stayed there, then I put some water on him, hit him, and he took knockback. For some kind of reason, if the entify is burning and you hit it, it won't take knockback, well, at least on villagers.

Steps to Reproduce:
1. Burn a villager or some mob
2. Hit it and check it doesn't takes knockback
3. Put some water on him
4. Hit him again, notice it does take knockback

 

Additional Info
This is not exclusive to burning, but any form of damage which does not deal knockback, including:

• Burning
• Sweet Berries
• Cactus
• Magma
• Lava
• Falling on Stalagmites
• Fall Damage
• /damage command
• Drowning
• Freezing in Powder Snow
• Poison damage
• Wither damage
• Damage from being in fire or on a campfire
• Getting struck by Lightning
• Entity cramming
• Suffocation
• Vexes dying by existing for too long / Player Starvation