Pretty sure this is an intentional thing, since it's been in the game since the beta tests and hasn't even been mentioned before.
I'm not exactly sure whether the decision to do this is meant to balance anything, I think it's mostly about the collision with a fire overriding the falling down simply because that's how the animations string together. After a certain point in your fall, you'll stop being able to be knocked out of your fall, so you'll literally fall in the fire and take extra damage.