Slime block can move and delete extended piston

Set up like the picture like below and press the wooden button. The slime block will delete the piston. What i see is the bottom piston get power and push the observer block, then observer block will power the top piston and push the slime block. When the slime block get push it take the bottom piston (extended) with it, when the piston retract, the slime block got pull and delete the bottom piston (extended).