1. Add RadPanel on to design time surface
2. Set its AutoScroll property to true
3. Add button which is partially visible
4. Try to scroll using the scrollbar

Resolution: 
You need to use RadScrollablePanel instead RadPanel. You can refer to link http://feedback.telerik.com/Project/154/Feedback/Details/109764-add-scrolling-behavior-for-radscrollablepanel-at-design-time