After an arrow hits a block, it can keep some of it's velocity from when it was fired after the block is either moved or removed.

Steps to Reproduce:

1. Place a trapdoor at eye-level to the player
   (Must be close enough to interact with the trapdoor)
2. Crouch
3. Shoot an arrow at the trapdoor
4. As soon as the arrow hits it, open the trapdoor quickly after

Observed Results:

The arrow will hit the trapdoor, coming to a full stop. Once the player opens the trapdoor, the arrow will sometimes jolt forward with gained speed and height.

Expected Results:

After an arrow hits an obstruction and comes to a full stop, it should lose all of it's velocity, and fall straight to the ground if the obstruction is moved or removed.

Screenshots/Videos:

My demonstration of the issue, and reproducing it:
MC-198908-1.mp4
Notice how the first arrow comes to a full stop, and falls as expected, where as the second arrow gains lots of momentum seemingly for no reaon.