StackTrace: http://pastebin.com/rzPwhcum

Crash when connecting Solid Redstone wire to Pistons. Quark is also installed with changes some stuff in the way Pistons work but it the NullPointer came from the Redstone Wire.

There were two wires in parallel in it crashed while disconnecting them by hand. One of them was powered and one wasn't powered, so the redstone power in the cables changed when disconnecing the two lines.

EDIT: This was on a Server.

Not 100% sure whether it's actually that bug, so better test this again once the next version is released.