Whenever I right-click in Opus all I can see is the drop shadow of the context menu but I can't see the actual menu. I can still click the menu and it will respond. I have tried uninstalling and reinstalling but it didn't help. It also does the same thing on the tray icon as well.
This has come up a couple of times (although not for a long while); it seemed to be a graphics driver bug. Try upgrading to the most recent driver for your video card (or, if you have upgraded recently, try rolling back to the previous version).