I searched for this issue, none was found, and so I'm posting it.
I doubt this was intentional but, when placing a torch on a block that is one-block higher than the Cobblestone Wall that is one-block adjacent to the block that you're placing the torch on, it causes the Cobblestone Wall to act as if you've placed the torch on the Wall itself. See attached screenshots for exact details.
Duplicate of MC-2349.