Put the summary of the bug you're having here

What I expected to happen was...:
I didn't think crash.

What actually happened was...:
I was in a obsidian room, with a blaze. I was in creative mod with a player in adventure mod. The blaze send a fireball on the obsidian. A Nether portal was created by the blaze's fireball and the game suddenly crash. That bug continued when a blaze sended another fireball on the obsidian and created a second portal. (A nether portal can do 23x23 blocks of obsidian)

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