While in Creative mode, moving towards a block and hitting the "Jump" key when the auto-jump feature activates, starts the player flying.

I believe it happens because, while in Creative mode, hitting the "Jump" key twice in quick succession toggles flying.
If auto-jump is registering as the "jump" key, and the user hits "jump" shortly thereafter, it would count as hitting "Jump" twice, and toggle flying.

I'm not sure if this is an "Intended Feature" - I certainly wasn't expecting it.