The bug

When you fire a firework from a dispenser and the firework hits a block, the firework slowly moves in the mid-air, even there are blocks that should the firework hit. When it finally hits a block and you remove that block, it gets completely stuck.

How to reproduce

1. Place a dispenser
2. Place firework with flight duration at least 50
3. Activate the dispenser
4. Wait until the firework hits a block
5. Remove that block
   → Observe that it got stuck in the air and slowly moves
6. Wait until it hits a block
   → It is now COMPLETELY stuck

In case you don't know how to give yourself that long flight duration rockets, the command is:

/give @p minecraft:firework_rocket{Fireworks:{Flight:50}}