Powering a piston from above will cause other pistons to fire, if they are immediately adjacent to the targeted piston.

I found this bug in Survival Mode, in a world that is shared by a dozen, or more, users. Our rail stations rely on rows of pistons and were malfunctioning (I really hope this gets fixed soon!).

I mocked it up in a Creative world to take snapshots. Am also including the Creative world as an attachment, so you can see the issue firsthand.