I couldn't stop to fall in spectator even I was pressing jump key.

I couldn't stop to fall in spectator even I was pressing jump key.
This happened in the SuperFlat world (single play).
I switched gamemode to spectator from creative, at (0, -60, 0).
Then I started fly, and went to the Y:-67, I couldn't stop to fall!
I think "this happened because I was enable 'toggle sneek'".
(This sentence was written by Japanese Player, so I cannot explain in English better.)