MDI control menu disappears when merging menus?

  Does anyone know why the control menu in an MDI application disappears
when a second window is opened.  Here's the situation:
  1) MDI Child form is maximized
  2) A 2nd child form is opened
  3) When I move the mouse cursor over the menu, the menu items shift left,
overwriting the control menu, while leaving the old menu text in the
The question I have is what do I have to do to either remove the control
menu altogether, or get it to work correctly for subsequent form openings?

Thanks in advance,