To reproduce: run the attached sample project and follow the steps in the gif file. When you start dragging, (i.e. when MouseMove first fires) there is a large jump to the position of the image.
Please refer to the attached sample project. If you drag a new shape or copy/paste an existing one it is not added to the DataSource collection as it is added in RadGanttView for example. Workaround: handle the ItemsChanged event and add a new record to the DataSource manually.