spark DataGrid drag move not supported

When draggin and and dropping items in a spark DataGrid in order to sort them, no dropindicator is shown and it is not possible to drop the items on a specified position. They alsways seem to be dropped before or after the selected item.
See attached example TestDDDataGrid

See example TestDDDataGrid2 for comparison. In TestDDDataGrid a mx:DataGrid is used. A dropindicator is shown and reordering is possible without any issues.