Using the supplied code results in a popup which is not draggable (8.0.4 nightly version). What sort of device are you encountering this on?
There is an idiosyncrasy of popups/modals where if ANY portion of the popup is rendered outside of the viewable area, then the popup becomes draggable. Is it possible that part of the popup you are opening is rendered but not viewable, perhaps due to scroll bars?