To reproduce:
-use RadForm with WindowState=Maximized at design-time;
-add RadPanel with Dock = Top;
-after running the application minimize the form and maximize it again; as a result the form title bar is cut off.

Workaround: set Margin of the FormElement and Top docked panel when maximizing:

private void Form1_SizeChanged(object sender, EventArgs e)
{
    RadForm form = sender as RadForm;
    if (form != null)
    {
        if (form.WindowState == FormWindowState.Maximized)
        {
            form.FormElement.Margin = new Padding(0, 8, 0, 0);
            (form.Controls[0] as RadPanel).PanelElement.Margin = new Padding(0, 20, 0, 0);
        }
    }
}