My bet is that one of the things which adds items to the context menu is going wrong inside of Opus and that's breaking context menus for the lister.
Not sure how best to track down where the problem is. The FAQ on context menu crashes has info on how to get a list of all the context menu handlers which are involved each time you right-click (which can include ones you don't see in the menu since they may still be asked if they want to add an item). It might be the last one listed before things break which is causing the problem, but that isn't guaranteed.
You may find the problem goes away if you remove all 3rd party context menu items except those you really want, as explained in here. It's be good to know what was causing the problem, though, so that a fix or workaround could be made.