If you have attached ContextMenu(RadContextMenu) to an element and you have added logic to drag this element with DragDropManager, when you open the ContextMenu and click on the element, a new DragOperation is started (it should just close the ContextMenu). Available in LIB version 2016.1.208, it will be also available in the 2016 Q1 SP1 Release.
After resizing the Window the buttons start working, but if dragged n dropped again, they stop.
Available in LIB version 2016.1.328, it will be also available in the 2016 R2 release.