If a player in Creative mode stands against a ladder that doesn't have a bottom ladder, and then holds down the jump key, they enter flight mode.

Steps to Reproduce:

1. Create a Creative world on a superflat
2. Build a two block high pillar
3. Place a ladder on the top block
4. Stand against the pillar
5. Hold down the jump key
6. Observe how you enter flight mode

Expected Result:

The player climbs the ladder normally.

Actual Result:

The player enters flight mode.