So, as far as I can see, it adds 0 attack power. Is this wad, is it only to use as a crafting resource, or is it just a bug? It seems like a waste of a rune to me.

Definitely a bug, in the guide it says its supposed to reflect damage.

I also have this problem.

I too have this bug. I don't know if it is like the Talos buff in Skyrim where it still works even though it gives a value of zero in the description. I just sell them to be on the safe side.

Confirmed bug, I've even tried using one before (found a Greater) and it does nothing. I'm holding on to them in hopes that when the fix comes, they'll be usable.