slime blocks clone

I was playing with the new slime block sticky piston thing. I set a sticky piston up to a comparator clock then attached a slime block to the piston head, and attached blocks on all sides to that. when i turned it on it ran for awhile then i turned around to look at some stuff, i look back and all the blocks on the slime block were "cloned" right beside the piston/on either side like the slime block. but all the original blocks were still moving on the slime block/piston thing like the were supposed to!!?
to get this bug follow the steps that i did. 🙂