When i watched a piston tutorial from Seth bling i spotted a bug. If you breaks an extended piston on the piston arm or the face of the piston it will drop a piston! if you breaks a un-extended piston wont anything drop.
I dont think that the piston was supposed to drop as an item.
Steps to Reproduce:
1. Place a piston (sticky or unsticky dosent matter)
2. Power it in someway, say with a redstonetorch
3. Break the piston on its face, the side that pushes.
4. That will drop a piston