Currently, when you click on a parent RadMenuItem in the Visual Studio designer, the popup with its child RadMenuItem is displayed. However, there is no way to hide the popup until the project is rebuild or the .xaml file is closed and opened again. This is troublesome because the popup is displayed on top of all Windows applications.
To resolve this, add code that handles the click outside of the menu (during the design-time) or add an option to avoid opening the popup at all.

Provide mechanism that allows the RadMenu to stays open when it lose mouse capture

Enable using checkable item with subitems.

Implement out-of-the box RadioGroups for RadMenuItems.