If you go to View > Switchbar and remove the check so that it's hidden, any windows that are minimized at the time will not have a corresponding MDI icon at the bottom of the screen. You can tell this isn't the intended behavior because as soon as you minimize a window that is visible, it gets its icon. The others are just lost (accessible from the Window menu though...)

This only happens with View > Switchbar. If you hide the switchbar from the Options dialog, the icons are there.

6.03 does not exhibit this behavior.

(I did try and make sure that the icons were not just scrolled off the screen or something; such is not the case)