Never mind... It's just as Adam said with the solid block under the torch. I just wasn't paying enough attention when testing.
This bug doesn't seem to always happen on all the side of a block, but just on what seems to be a (or a few) random side(s). That's what it felt like in my two worlds I tested it on at least.
Never mind... It's just as Adam said with the solid block under the torch. I just wasn't paying enough attention when testing.