Redstone mechanisms only update when the block ID is changed

Blocks that accept redstone power will only update if the block ID of the block providing the power is changed, not the data.

For example, place a lever and turn it on. Place a redstone lamp next to the block the lever is on. Use the setblock command to set the lever to air. The lamp will update, and turn off. Repeat the experiment, but instead of setting the lever to air, set it to a lever in the "off" state (or any state that isn't on, an invalid state where the lever isn't attached to anything also works). The lamp will not update.

This only occurs if the block providing power is not right next the block receiving the power. It will occur with any object that provides power, not just levers.