Observers redirect redstone although the texture does not show this situation

When you ACTIVATE a redstone compoment using an observer, the redstone compoment does not react to anything. This is because observers redirect redstone, but the texture does not show it.
To recreate it, place an observer with redstone in front of the output. Place a block to the left of the redstone and place a piston next to the block. Make a block update to the input of the observer, and you will see the piston does not get powered.