Let's say I have application with two forms (main, and secondary). Secondary form has altered CreateParams (so form could have taskbar button), and it can be minimized to taskbar. Both forms are opened and visible on screen. Then we must open another app, let's say notepad.exe. If we shake notepad window (left-right) -> aero shake will activate and it will minimize all forms that can be minimized. Unfortunally there is a problem because extended border of our secondary form stays on screen (clientarea is minimized, only border remains). If we click on that border it will vanish. I can prepare demo app but it can be easily reproduced by yourself.