image returned from QtWin::fromHBITMAP display weird

Sample1:
1: use IShellItemImageFactory::GetImage on a spcified file or folder, got a HBITMAP object
2: pass this HBITMAP object into QtWin::fromHBITMAP, got a QPixmap object
3: show this QPixmap in qml over QQuickImageProvider
4: I found some weird white area in image

Sample2:
1: still, use IShellItemImageFactory::GetImage got corresponding HBITMAP object
2: then just open a dialog which hash a STATIC control, show HBITMAP on that control
3: image is clear

Result:
the attachment is a comparison image .
left side is the result of Sample1.
right side is the result of Sample2.

Is that a BUG? thanks for your time

--------------------------- More Information -------------------------------
1: you can build sample1 & sample, they are complete
2: run them with command line , usage: xxx.exe [ small | medium | large | extralarge ] [ file | folder]
3: I know why there existed weird white area in image:
A: after using QtWin::fromHBITMAP, the the image's background is white , not transparent
B: draw HBITMAP on a static control with win32 api, it's background is transparent