Keep the Dropdown with Input Element While Scrolling
The user scrolls the page when the drop down is already opened.
When the RadComboBox control is placed within a scrollable container and user tries to scroll with the mouse and the drop down is opened, the drop down element "freezes" and stays on same spot on the screen while all other elements scroll with the page.
Please refer to the following code library resource. You will find attached a sample working project with some instructions.