Once I caught on fire and accidentally fell off of a high cliff. I thought I was going to die but I took NO fall damage. It is not that easy to reproduce. It only sometimes happens.
To reproduce, Catch on fire and jump off a tall tower or into a ravine. Sometimes it will not work. Keep doing that process until it you take no fall damage.

Expected result: You will take fall damage when you are on fire.

Actual result: Sometimes you don't take fall damage when you are on fire.