When there is a piston pointing up with a redstone dust on a half slab next to it, it will not extend when a redstone block is placed on top of it even though it looks like redstone is pointing into it. Updating the piston doesn't change this.

This is what happens when there are two pieces of redstone dust pointing into the piston. It also happens when the second piece of redstone is replaced with a repeater/lever/button.

I am assuming this is because the redstone block does not make the redstone dust point into itself, even though it looks like it does. I assume it goes from the middle to the right, even though it shows that it is going from left to right.

What I expected to happen:

The piston to either extend or not extend in both cases:

What happened:

The piston extended in in one case, but not in the other.