Detector rails giving power without minecarts

When you place a detector rail, the block below the rail receives strong power (powering the blocks to its sides and below it) and the blocks to the sides of the detector rail receives weak power. This only happens when the rail is set down (without minecart) and the blocks are given a redstone update. The same goes for when the rail is destroyed, the blocks will only stop receiving power when they are given a redstone update