Mmm... it IS a problem of VWMHideTaskOnSwitch. If I disable it, it works fine, but then I don't have a desktop dependent taskbar. For the moment I will have to choose between the best of two evils ;-)
Adding *VWMFix SmartSketchMDIFrame (found out using WinSpector this is the window class for Flash MX) doesn't change a thing.

(Is it hard to understand the source codes? I have quite some experience in programming, albeit platform independent.)