netherack doesn't burn forever

Put the summary of the bug you're having here netherack doesn't burn forever

What I expected to happen was...:
Describe what you thought should happen here the fire on the netherack permanently

*What actually happened was...: the fire stayed for a bout 20 seconds
Describe what happened here

Steps to Reproduce:
1. Put a step by step guide on how to trigger the bug here
2. ...
3. ...