Affects Version/s: Minecraft 14w28a
Fix Version/s: None
Operating Version 6.2
Operating System 64bit
Java Version 1.7.0_45
When a piston is set on a timer, simply walking up to the front of the piston and walking forward as the piston retracts will allow the player to walk directly through the piston. As far as I found this only applied to Normal Pistons and not Sticky Pistons.
To recreate: Place down a piston and connect it to a redstone timer going at any speed, it is much easier to do this at a lower speed, however it seems to have worked at any speed I tried. While the piston is unpowered, walk directly up to it. Once the piston extends walk forward slightly and you will move a bit forward, as the piston retract continue walking forward and the arm of the piston will carry you through the block as you walk.
(Pictures are uploaded in order of 4,3,2,1)