Players standing right next to blocks don't receive vertical knockback if attacked by anything that isn't a player. Players do vertical knockback to other players as one would expect.

It seems like knockback is only being applied incorrectly if the wall that the player is standing against is no higher than one block.

How to reproduce

• Stand as close to a wall as possible
• Let an entity, a zombie for example, hit you towards the wall
• Watch as you don't receive any vertical knockback