DVD/Home Theater issues

I have a 2012 Tiffin Red, and my DVD player started acting up a few months ago. It seemed like it would only play perfect or new DVD's. If we tried a Redbox movie that wasn't perfect, we only got sound and a blue screen. No picture. Because I wanted something that would plug right into the connections in my AV cabinet, I bought the exact same Panasonic model on ebay and hooked it up. For some crazy reason, when I hit the Open/close button on the player, the door will not open unless I unhook the HDMI cord. This is the craziest thing I have seen in awhile. If I unhook the HDMI cord, the door will slide open, and when I put the DVD in it, it closes and begins to play. To get the picture, I have to plug the HDMI cord back in. But when I stop the movie, the door won't open again while the HDMI cord is connected. But as soon as I unhook it from the back of the player, the door will open again. I realize that the HDMI cord should just be giving me the video, but it is somehow affecting the DVD door. Anyone have an idea? Thanks
Bill