Is your screen a manual pull-down? I have the manual Da-Lite Model C high-contrast matte white paired with a Panny PT-AE4000U and I do have similar issues due to it being a manual screen that is not perfectly flat. The, albeit, small "hills and valleys" do cause, what I call, shadows that are barely noticeable during still scenes, but are during horizontal pans. Especially on brightly lit ones like a pan across a desert or the sky. But like I said, I don't really notice them during still bright scenes.
Actually, I'm getting ready to get rid of my Panny for the Epson 5020UB so I'd be curious about what others will respond to your situation.