When a powered piston has a powered redtone diagonally on top of it it like locks its position until you break a block in front of the extended piston.
MC-4124
Piston Update Bug
Resolved
Duplicate
0
multinfs
(Unassigned)
Unconfirmed
extended, piston
Minecraft 1.4.5
Retrieved
Duplicate of MC-108 , please use the search function to see if your bug has already been submitted. Currently over 30% of tickets are being closed as duplicate.