What I expected to happen was...:
Piston should retract like it normally has in the past.

What actually happened was...:
The piston would remain extended until I gave it a "block update" by either removing a block next to it or placing one next to it. (There was no nearby power source for the piston to remain powered by)

Steps to Reproduce:
(SEE PICTURES BELOW FOR A MORE IN-DEPTH LOOK. It is somewhat hard to explain)

1. Place a couple pistons facing downwards in a 7x7 grid, with 1 block of air between each. (4 pistons with 3 blocks of air)
(note: the "grid" is more of just to cover more of an area to show that only certain block areas create the glitch piston)
2. Build a "pitchfork" above the pistons to connect them all by redstone (see pictures below for exact example)
3. Turn lever on, all pistons will power perfectly normal
4. Turn lever off, all pistons will de-power, but some will stay extended. (Pistons that stay extended will actually vary based on location of the build).

Note: This is a singleplayer world with NO MODS installed at all, and a brand new generated minecraft map. I discovered this little glitch/bug while playing on a multiplayer server building a redstone puzzle minigame for the players. I had originally thought it to be something with a plugin server-side but after testing in a singleplayer world I found it to be a glitch caused by 1.6.1/1.6.2 version of minecraft. It had worked perfectly fine in earlier versions (I had a similar build in 1.5 that never malfunctioned like this)

1st image: showing the grid
2nd image: Showing the "pitchfork" and redstone
3rd image: Showing the "powered" piston with no power connected to it
4th image: Different location of "glitched" pistons showing how more of them glitch.
5th image: Overhead shot of 4th pic to show no redstone is powered.