enchantment:Fire Aspect in 13w36 &13w37a isnt working as it should

Put the summary of the bug you're having here

What I expected to happen was...:
things to burn to death

What actually happened was...:
nothing

Steps to Reproduce:
1. Put a step by step guide on how to trigger the bug here
2. ...enchant get fire aspect I or II
3. ...punch a mob with the sword doesnt burn?