Note: I do not know how to recreate the event. All that I know is that sometimes when I use redstone in small areas, it glitches my piston and extends it permanently.
I also make sure no redstone can hit it by surrounding it with glass. I am in singleplayer

Video I posted on youtube about what it looks like:
http://www.youtube.com/watch?v=kL9ccQSUcJ8&list=HL1364960297&feature=mh_lolz