As it's easier to show with a video (would take longer to read a description), one is provided. Two related/similar bugs present.
Related issues
Comments
migrated
MC-13352
Piston retraction/extension bug with diagonal pressure plate
Resolved
Duplicate
0
migrated
migrated
(Unassigned)
Unconfirmed
piston, redstone
Minecraft 1.5.1
Retrieved
153rd Duplicate of MC-108, please use the search function to see if your bug has already been submitted. Currently over 55% of tickets are being closed as duplicate.