Workaround - when RadPane is activated bring its ToolWindow to front. Hook to ActivePaneChanged event and implement the following handler;

private void RadDocking_ActivePaneChanged(object sender, ActivePangeChangedEventArgs e)
{
    if (e.NewPane != null && e.NewPane.IsFloating)
    {
        var toolWindow = e.NewPane.ParentOfType<ToolWindow>();
        if (toolWindow != null)
        {
            toolWindow.BringToFront();
        }
    }
}