When you try to break specific blocks on the debug world it will instantly crash my your minecraft. Some of these blocks are furnaces, top half of wooden doors.
Side note: When right clicking on certain comparators it spawns in around 15 stacks of comparators.
Environment
OS: Windows 7 (ver 6.1, arch x86)
Java: 1.7.0_55 (by Oracle Corporation)
Launcher: Minecraft Launcher 1.4.4 (bootstrap 4)
Minecraft: 14w27b (updated Wed Jul 02 12:34:56 MDT 2014)
Don't do that then. The debug world is only for observing how all the blocks in all their possible states render, generally for testing resource packs. You're only supposed to be in spectator mode in the debug world.