Extended piston head not removed when /setblock is used to place a different piston base.

Found this bug with /setblock and (Sticky)pistons.
Steps to reproduce:
1. place a redstone block anywhere.
2. place a temp block next to the redstone block for where your pistons are going to go.
3. use /setblock x y z minecraft:piston[facing=up] at the temp blocks x,y,z.
4. do step 3 again (at the same x,y,z) but change 'up' to east, west, north, south or down
when you do this you'll end up with a piston with 5 heads destroying any one of them will destroy the whole thing.
i was trying to use the /setblock for a 2 story maze and i ran into this, was expecting the previous piston(and piston head) to be replaced, not become a multi-headed piston. kinda broke my maze.