When wiring with redstone, there is a bug involving passing redstone adjacent to a lamp. If you have a redstone lamp running parallel and adjacent to a line of redstone wire, the block adjacent to the redstone lamp will remain powered. The redstone lamp has to be powered with a repeater, and the wire has to be parallel to the powered lamp. The wire has to also be connected to the wire that initially powered the lamp. I believe it has something to do with the behavior of redstone lamps to power the block adjacent to them, regardless of it being a lamp or not. I've done extensive testing of this after discovering it, and the attached picture is the densest form of the bug. Note that the lever off to the left side is in the OFF state.