windows beneath not being painted when using a layered window

I will try to explain my problem the best i can,

I'm creating a layered window in c++ (using windowsXP), all works fine until i drag my created window near the windows start button, and then when i press the star button of windows taskbar and close it again all the windows beneath of my layered window aren't being painted (only in the area of the start window that pops over my window).

My create window is like this:

CWnd::CreateEx( WS_EX_TOOLWINDOW | WS_EX_LAYERED, AfxRegisterWndClass(0), lpstr_name, WS_POPUP, 0,0,0,0, pc_parent->GetSafeHwnd(), 0);

...

When i create the window with this styles the problem ocurrs, but if i create with the extended style WS_EX_TRANSPARENT and all the others the problem does not occur any more. And if instead of a WS_POPUP window is a WS_CHILD or WS_OVERLAPPED then this also doesn't occur...

Can anyone please explain why when i create a WS_POPUP window with the WS_EX_LAYERED style all the beneath windows aren't updated, and if i add the style WS_EX_TRANSPARENT this works fine.

Note: why i do not use the WS_EX_TRANSPARENT style if it works right? if i use it then my window can not be dragged and i need it to do it :)

Updated: alt text http://img17.imageshack.us/img17/586/clipboard01il.jpg

The image above is to describe better what is happening: The first part of the image you can see my leyered window and beneath is the vs, in the second img i press the start button and then in the last image i already drag my layered window to the right and you can see that the vs开发者_Go百科 window does not updates the affected area. Note that this situation until now only occurs with the start window?! with other windows it does not happen!?...

Thanks

---

only in the area of the start window that pops over my window

That's expected. Only that clipping rectangle is obscured by the start menu so only that region will be repainted. What behavior are you expecting? If there are windows covered by more upper level windows, then they won't be repainted either -- why repaint something just to paint over it?

All underneath windows need to get repainted though if you use transparent because GDI can't calculate the final color of the pixel without knowing the area below the window's color.