This affects any version when it involves player to player combat. So when your opponent hits you, you normally take horizontal knockback like you normally should. But when your opponent hits you and you jump at the same time they hit you, instead of taking horizontal knockback, you take vertical knockback. It's essentially jumping in the air while being hit and heavily reducing knockback. This mechanic became known as "Jump Resetting" and has been used in the combat system for over a couple years now. 

I certainly believe this is a bug incorporated into the game where when you are getting hit and you jump, the game registers that you're jumping instead of taking horizontal knockback like you would when you get hit and also not being on the ground when you jump.  This mechanic also affects bedrock edition.

Videos demonstrating it: https://www.youtube.com/watch?v=zHiBxcv1t-Q 

https://www.youtube.com/watch?v=BFKSkErS6rU