Summary says it all. To reproduce this bug do these steps:
- Disable Auto-Jump in Settings > Controls
- Open a [new] world (older worlds should be affected too)
- Walk towards a block and keep pressing W (or UP or your "walk forward" key)
- Try to press SPACE (or your "Jump" key)
- You'll notice that your character will not jump and stay in place
It's so frustating, because you have to walk a bit back and then jump and go forward.