Windows 7, java version 7 update 51
I was making a redstone 3x3 door in the new snapshot when one of the sticky pistons started reproducing a new sticky piston.
What I expected to happen was the piston to pull and push the slime block over and over.
What actually happened was the top piston would pull back sometimes and create another piston behind it.
Steps to Reproduce:
1. create a stair step of three sticky pistons
2. wire all pistons up to a redstone signal
3. make sure that top piston is pulling and pushing a 3x3 wall of slime blocks
4. hook the restone up to a redstone clock and the top piston will in about 10 cycles produce a piston on the back of it.
further steps on how to reproduce is in video attached.