Steps to Reproduce:

       1. Place an upside down stair.

       2. Start flying.

       3. Put your head in the stair.

       4. Try to start/stop flying.

Observed Results:

As long as your head is in the stair, you can't start/stop flying (unless you change gamemode to stop).

Expected Results:

If you were trying to stop flying, you should drop back to the ground.

If you were trying to start flying, you should do so.

Screenshots/Videos attached: https://we.tl/t-H0215WDuhg