The best way to reproduce this issue is to click File menu and move the mouse cursor to the right to show all main menus quickly, i.e. File, Edit, View, Insert... First a black rectangle for the menu is shown before the menu items rendered. This issue also happends when opening a dialog from a menu or by visiting different tabs on the sidebar to the right. I couldn't remember whether this issue is new or also applies to 5.0.2.
*** This bug has been marked as a duplicate of bug 94726 ***