I found this bug when I tried to make compact minecart elevator.

What I expected to happen was...:
What I expected to happen was that the powered rail in the middle would be updated and unpowered. The rail have been updated, but not unpowered.

What I actually to happen was...:
What actually happened was that the middle rail is powered. The rail is powered until it gets a blockupdate.

Steps to Reproduce:
1. Build the iron like I did in the screenshot. One side MUST be pointing at north and the other side at south.
2. Place the torch, at the south side of the iron blocks.
3. Place powered rails where you can see the powered rails on the screenshot and NOT where the unpowered rail is.
4. Place a rail of any kind where the unpowered rail is on the screenshot.
5. Now you have the bug! If you have placed a normal rail in step 4, you can destroy it!