Double-pressing spacebar to ascend in creative or spectator mode does not work when Sneak Toggle is enabled and instead the player floats downwards and if in spectator mode, eventually falls out of the world.

To replicate, in either creative or spectator mode:

1. Enable Sneak: Toggle
2. /tp @p ~ ~100 ~ #Move up 100 blocks
3. Double-tap spacebar to stop falling
4. ❌ Player continuously floats downwards

 Update: This may be considered expected behaviour as I didn't realise at first that sneak toggle had actually activated. If you deactivate sneak by pressing shift you are able to ascend again. It looks like the combination of a toggled sneak in progress and the spacebar for ascending will override each other causing the player to stay stationary until the ascend (spacebar) is cancelled and the sneak (descend) resumes.

Possibly a little counter-intuitive since unless you are on the ground, there is no sneaking so what is actually happening is the shift key bind is being toggled rather than the act of sneaking. This is also confusing because there's no key toggle for ascending.