When a block changes the direction of a powered redstone wire, the redstone won't power any block.
Though, the orientation doesn't seem to be important ; I first noticed this bug in 1.6.2.
Images (1 & 2) : before and after the redstone block gets placed ; notice on the second image that ONLY the redstone lamp which is in the axis of the wire is powered, the other one isn't. Updating the unpowered lamp doesn't change anything.
Images (3, 4 & 5) : If you change the direction of a redstone wire by placing a block, the redstone won't power any block/system. Though, a block update can affect the result.
Video here :