Summary says it all. To reproduce this bug do these steps:

1. Disable Auto-Jump in Settings > Controls
2. Open a [new] world (older worlds should be affected too)
3. Walk towards a block and keep pressing W (or UP or your "walk forward" key)
4. Try to press SPACE (or your "Jump" key)

1. 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.