Retain size after minimized or maximized

[George]

I have a MDI parnet form and several child forms in my project. I follow the example here to deal with the minimum size problem of MDI child form.
(this one http://www.syncfusion.com/FAQ/WinForms/FAQ_c4c.asp#q824q )

But after I made the change, the child forms cannot retain original size after I minimize or maxmize it. It just shows in its minimum size.

Does anyone know how to deal with this problem?
Or can anyone tell me how to catch the click event of minimize and maxmize box ?

Thanks in advance.

George