Parallax issue with this scope - Mueller Optics 8-32x44mm Side Focus Target Dot Rifle Scope

I was excited to get my new Mueller 8-32 Target Dot scope for my .22lr bench rifle. I installed it and shot it on the range and was a bit confused. My previously accurate rifle was having accuracy problems (shooting at 50yds). I went on RFC and took the advice of my fellow members there and checked everything on the rifle. Other than needing a good cleaning, everything seemed fine. Today, my accuracy went bad again, from 0.2-0.3 inches to 1-1 1/2 inches. As I was troubleshooting this at the bench, I noticed that my point of aim was moving over a full target's width with the movement of my head (ARA target). The rifle was on a front rest and a rear bag at the time. I tried readjusting the parallax but it made no difference. If the sight picture was clear, the point of aim moved with any head movement. It is past the return window for Optics Planet, but I have notified Mueller Optics to ask for an RMA to have the scope repaired or replaced. I know it's not a real expensive scope, but many reviewers have had no problems. Just my luck, I guess.