When placing a door with redstone paste under it and removing the paste was how it was triggered. Seems to happen with any item from redstone paste.

http://pastebin.com/uTSrnhSd

Changing door void auto fill to false will fix it from happening but not fix broken worlds.

Thanks for report. I've had a similar one before, and will look into how to prevent this from happening.

Added some new code to hopefully stop this crash, and a limit to multiblock size in the configuration file. It will be included in the next dev release either today, or sometime this week.