When powering two vertical pistons at the same time, they both extract with one reaching into the other and only one "stone block part" being invisible, so it basically shows as one stone block with two extended pistons:
http://www.youtube.com/watch?v=_kfJo3kC3uA
MC-8929
Piston glitch
Resolved
Duplicate
0
Michael Kliehm
(Unassigned)
Unconfirmed
piston
Snapshot 13w05b
Retrieved
Duplicate of MC-8198, please use the search function to see if your bug has already been submitted. Currently over 50% of tickets are being closed as duplicate.