iTunes does not work with WS_EX_LAYERED

Hello

I am developing certain project which requires almost all windows to be layered (WS_EX_LAYERED extended style to be set), then I call WinAPI function SetLayeredWindowAttributes on them. This correctly works for all applications but not for iTunes (tested on Win8 x64). When I set WS_EX_LAYERED flag to iTunes application window, only window shadow is visible and the window completely disappers.

Thus I would like to ask why this happens???

On the other side, iTunes is one of the applications where I don't have to set WS_EX_LAYERED (because it does not use default DWM window border), so is there any flag/bit/settings which is different for iTunes and other applications so I can easily differentiate them (except the condition like "if window == iTunes") ???

Thanks in advance for any help!