There is a bug in the 1.5.2 pre-realease and the 1.6 snapshot, where the redstone freeze in "The End" after the chunks getting new loaded.
I mean not the "normal" bug where only the repeaters freeze, all kind of redstone, like buttons and rail-detector.
So for example: place a block with a button and go a few blocks away that the chunk with the button get unloaded.
Get back and press the button, the button freeze for a random time.