Put the summary of the bug you're having here

What I expected to happen was...: 
Be able to jump when right up against a block

What actually happened was...:
It tries to jump, looks like the animation starts but it wont allow you to jump, in creative it sometimes puts you in flying mode, in survival you cant jump

Steps to Reproduce:
1. Walk up to any one-high block
2. Be right against the block
3. Try to jump, nothing happens