Determine whether Selector.SelectionChanged event was initiated by a user

Simple work around:

You could create a method that temporarily disables the SelectionChanged event and call it when you need to change the selection programmatically.

private void SelectGridRow( int SelectedIndex )
{
    myDataGrid.SelectionChanged -= myDataGrid_SelectionChanged;
    myDataGrid.SelectedIndex = SelectedIndex;

    // other work ...

    myDataGrid.SelectionChanged += myDataGrid_SelectionChanged;
}