To reproduce:
- Add 3 radio buttons to a user control.
- Set the ToggleState of the second radio button to  On.
- Show the user control in a DockWindow.
- You will notice that the first toggle button is selected.

Workaround:
Set the toggle state after the window is added to the RadDock
void radDock1_DockWindowAdded(object sender, Telerik.WinControls.UI.Docking.DockWindowEventArgs e)
{
    if (e.DockWindow.Text == "UserControl11")
    {
        UserControl1 uc1 = e.DockWindow.Controls[0] as UserControl1;
        ((RadRadioButton)uc1.Controls[1]).ToggleState = Telerik.WinControls.Enumerations.ToggleState.On;
    }
}