I have had several instances where redstone wires and powered blocks will randomly disappear from my SSP world. (Started earlier than 1.4.4)

Sometimes, when I interact with them the components will drop as items;
i.e. walking up to an iron door with pressure plates on either side, stepping on one plate caused the door and both attached plates to drop as items.

Other times when I log in, they have simply vanished, i.e. redstone wire attached to dispensers in my chicken farm and the attached buttons are no longer present when I go into the room where they once were (also, a TNT cannon of mine loses all redstone wire/repeaters/torches/nearby trapdoor).