Detector rails, which were activated by a minecart upon them, keep their active-state when moved by a piston, although there isn't minecart upon afterwards.
Detector rails affected by this bug can't be manually reset to normal function, they however change back to normal function after a certain time.

What I expected to happen was...:
As there is no minecart upon them any more, after movement the detector-rail should change to off-mode.

What actually happened was...:
Instead, the detector-rail keeps it's on state for a certain time.

Steps to Reproduce:
1. Place a minecart on a detector rail
2. Move the detector rail (horizontally) with a piston
3. The detector rail stays on unexpectedly, although there is no cart on it.

Update (16.2.2013)
As noticed by user kbk, not only the rail's state is messed up, when the detector-rail is moved, but also the underlying block does not get/send it's updates properly too.