When you hit an endercrystal, the fire it makes does not get put out, even if the block below gets destroyed. You can make floating fire this way, but water or placing blocks in the fire can put it out. Also, if an EnderCrystal is not in a block (the endercrystals in the end are actually partially inside the obsidian) it will create a some lag. It dropped me from 60 fps to ~40 fps.
Steps to Reproduce:
1. Find (or create) and endercrystal
2. Destroy it.
3. You will find the fire is eternal, unless you put blocks where it is.

For endercrystal lag bug:
1. Find an endercrystal
2. Carefully remove all the obsidian around it. You will find a block inside the endercrystal.
3. Break that block and lag to death.
1st picture: floating fire
2nd picture: notice the lower FPS and the endercrystal is not inside a block