"onrowdropping" event fires after clicking an already selected grid item (no drag and drop involved). You can see this behavior in your demo: http://demos.telerik.com/aspnet-ajax/grid/examples/columns-rows/rows/drag-and-drop/defaultcs.aspx
I am running into this issue as well ( or something similiar ).......... row in radgrid fires OnRowDropping client-side event when I click on a row in the radgrid