Pistons (both standard and sticky) can remain extended when not powered.
If you power a piston from above, then destroy the redstone powering it, it will remain extended in some circumstances where it does not have anything powering it. (see attached video for clarity). I have also seen this happen when switching power off to the piston, if there is other powered redstone nearby.
VIDEO: http://youtu.be/mWb6oj2TxyY
The video was initially created for a Bukkit ticket, before finding out the issue existed outside of bukkit.
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I don't see how this duplicates 108, as this reports that the intended feature is not working correctly, while the other complains that the intended feature shouldn't be there. I just don't see how having pistons remained powered after removing ALL nearby power sources isn't a bug, unless pistons are just supposed to magically have infinite power.
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This is the BUD-effect
Destroying activated redstone causes a lesser radius of block-update than unpowering the redstone.
And with this technique you could create one-time BUDs that don't take up much space
Original report with Bukkit: https://bukkit.atlassian.net/browse/BUKKIT-4394