Hello JSW W.,
I assume that you mean the case when along with NCommandBarsManager and NMenuBar you have also NDockManager and NUIDocuments which view is set to MdiStandard.
You should have this "Doc" icon and "X" on your menu bar when some of the documents is maximized.
They appear to be able to minimize or restore the maximized document.
Best Regards,
Nevron Support Team