I have in my world a small 1 by 1 hole next to a wall, where I usually jump to reach some chests. Normally I sprint towards the hole, to save some time. I noticed, that if i sprint into the wall without jumping, I will stick to the wall, and decend very slowly, super meatboy style. While decending, I'm able to jump, but that returns me to normal fall speed. 

I then tried to do the same up some stairs I had nearby. The stairs were two blocks wide, and two blocks deep. From upstairs, I sprinted towards the stairs, and upon arriving hit the wall at a strong angle. The best way to describe what happened would be by saying: I ran down the wall, Prince of Persia Style. I'm not going to lie, I had some fun with this bug.

To recreate this bug, all that is needed is a 1 block long hole ( width and depth don't matter) in front of a wall, and then to sprint against that wall at a slight angle, such as if the intentions were to drop down the hole. The bug will happen if the player doesn't release at any point the W key. Pressing other keys during the fall, or moving the mouse slightly to the sides doesn't have an effect on the fall. This experiment fails sometimes, but i cant explain why.

Ps.: Please don't remove this, and if you do, please consider bringing it back in 1.15. It is a lot of fun.