I replaced my brake pads all the way around but when I got to the last one, (left rear) the piston wants to stay out? No leaks at all. What would make a piston want to stay out? I push it in and it comes right back out. It not hard to push in but it does go easy with a small c-clamp…..

To get it on the disc I had to spread the pads with a screw driver?