being able to walk through piston extenders

with 2 pistons stacked ontop of eachother, you can walk through the extenders

What I expected to happen was...:
you normally cant walk through piston extenders

What actually happened was...:
walked through the piston extenders

Steps to Reproduce:
1. stack 2 pistons on top of each other and activate them
2. have your character lined up and head straight forward to the grid
3. walk forward