*Sorry for my bad english*

The bug happen when you put a redstone torch on a block and that you remove that block. The torch will stay there. Even if you make it update. It does'nt work with normal light torchs. It do it only if there is another block beside de torch. It will not work if the torch "could" not be attach on another block. So, in fact, the torch will stay if there's another block where it can normally be attached. In fact, it's just a graphic bug.

Step-by-step :
1. Put a solid block anywhere... It can even be a redstone block.
2. Put a redstone torch on any side, but not on top.
3. You also need to put blocks on any other side (or below) the torch. See the pictures.
4. Remove the block where the torch is, you can even put a power source such as the new redstone block, it will act as normal.