The Bug:

In certain circumstances, redstone dust will remain powered despise there being no power source.

This may be caused by chunk borders

How to reproduce:

• Download the atteached world. There will be a complicated redstone contraption, but only a couple of block matter. On the bottom right, there is a redstone dust on lime concrete with a sign on it.
• Flip the lever in front of the diamond blocks once.
• Wait for the redstone to calm down
• Flip the lever again, pay attention to the aforementioned redstone dust
  • Notice how the redstone dust stays powered despite there being no power source
• Place a block next to the redstone dust
  • This will give the redstone dust an update, causing it to depower, but only when updated by a player