So, you want to prevent dragging the editing currect cell? If so, you can try handling the QueryCanOleDragRange and cancel it there.
private void gridDataBoundGrid1_QueryCanOleDragRange(object sender, GridQueryCanOleDragRangeEventArgs e)
{
if(this.gridDataBoundGrid1.CurrentCell.IsEditing)
e.Cancel = true;
}