This is a VERY nasty bug and REALLY needs to be fixed.
Please fix this bug. It is a REAL pain in the neck. We have a world implemented with an extensive rail system and ALL of our rail stations use push-button panels to set the rail switches. The push-buttons are supposed to activate the piston below them, in order to drive the circuitry that sets the rail switches. This has worked flawlessly ever since the official release, but now it is all broken because pushing one button now causes multiple pistons below to fire.
I wrote up MC-11957, which was quickly deemed a dupe of MC-108, but in fact it is exactly the bug described here.
In my example, I used buttons to fire the pistons. Rows of pistons above and below a row of buttons. Select a middle button, and one piston above fires. Unfortunately, three pistons BELOW will also fire. This is a big change of behavior.
I can confirm that this issue is still a concern with the distributed 1.7.10 client and the 1.7.9 server versions of MineCraft. Beyond that, I am unable to provide any more information at this time because I am currently traveling.