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:

• Place a trapdoor at eye-level to the player
• Crouch
• Shoot an arrow at the trapdoor
• Open the trapdoor

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.