Flight mode is disabled when flying under stairs and hoppers

Steps to Reproduce:

1. Place a stair a few blocks in the air
2. Fly under the stair

Observed Results:
Flight mode is disabled.

Expected Results:
Flight mode remains enabled.

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The video shows: When a player passes inside an inverted step, the player's flight mode is automatically disabled. Or when the player enters the flight mode and passes into that part of the inverted step, the flight mode is also disabled.