in Delphi TIPS :: When you minimize an MDI child form in an MDI Delphi application - the "window" appears as iconic inside the MDI parent container form. This, pretty much, looks weird.
To hide the minimized MDI child window, you must trap its WM_Size message...
Read the full article to learn how to Hide Minimized MDI Delphi Child Forms.
Related:
There should be a Msg.Result := 0 else inherited; in the WMSize handler.
Andreas, thanks for the hint.