In my server when i place redstone torches and work on something else while on the same chunk the redstone torch can sometimes flicker even when on its own.
I think you encounter the same bug as mentionned on this topic :
Which answer was :
This is a know bug, all you can do is restarting your game. It happens sometimes on random blocks, and it will never work again on that block until you restart. It happens both on single and multiplayer, we hope it will be fixed on 1.8