I made Minecraft crash while trying to experiment with hash problems!
Of course, that is expected when the items on my hotbar are all cheaty variants (the actual block version of Redstone and repeaters), and I am moving locked chests with pistons... To reproduce, you must reactivate the clock, then stand on the vertical piston. Very interesting bug, probably a side effect of the behavior that was what I was experimenting with. Depending on whether the vertical or horizontal piston is instantly pulling, the crash is easier. Just stand on the block if vertical. My test world constantly crashes now. This device is weird.
To use this world, you may need to delete the level.dat and then go to my coordinates.
The locked chests are probably not required, I just was messing around. Doesn't work with solid blocks, it may need locked chests. Still experimenting.
This has NOTHING to do with quasiconectivity.