I recently got a PX-750 off Ebay with some damage to the case. I have it all put back together but am experiencing an issue with the sliding key cover. The problem is that it scrapes the top of the control faceplate. As far as I can determine everything is where it's supposed to be, nothing is broken. Is it just a bad design and that's what happens or is there some other issue? Maybe some piece that's missing that prevents this?