Crash when clicking customize when selecting superflat

I loaded Minecraft, pressed Single Player, and to test the new features, I like using a superflat world. I selected superflat world, then to click customize, so I could use the Redstone Ready preset. I've tried it 3 times, just to make sure it wasn't a fluke, and all 3 times it crashed. I didn't get time to do a test on the other snapshot versions.

Ellis

I'm not sure how I could get screenshots, so I apologise.