When 2 pistons try to push a block so that when both heads are extended the block in the middle will be destroyed if placed on one piston and not the other, works facing both directions, Not a massive problem. If there was not a good explanation I uploaded a bug report to youtube.
Link: http://www.youtube.com/watch?v=_n0MjCOQmek&feature=youtu.be
Environment
Stone flatworld - Redstone test world
Duplicate of MC-5774, please use the search function to see if your bug has already been submitted. Currently over 50% of tickets are being closed as duplicate.