When mining redstone ore using a silk touch pick, it will drop 2 different ore blocks that don't stack. One would be an "ON" state ore and the other an "OFF" state ore. You can tell which is which by placing the ore on the ground. To recreate, use a silk touch pick and mine several packets of redstone ore.
Comments 4
I was able reproduce, but only in the rare case that a redstone ore deactivated while mining. Because mining them also activates them. Tested in SP and MP. In MP it was more likely, maybe because due to lag?
Unable to reproduce.