Why do bitmap images flicker in single threaded MFC applications even though there is no chance of parallel access to/from Bitmap buffer?

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MFC

Hi,

Here is a small code snippet:

class staticbitmap : public CStatic {
    // ...
};

staticbitmap pic[4];

hbm[i] = (HBITMAP)LoadImage(NULL, filepath[i], IMAGE_BITMAP, 0, 0,LR_LOADFROMFILE|LR_CREATEDIBSECTION);
GetObject(hbm[i], sizeof(bm[i]), &bm[i]);
buf[i] = reinterpret_cast<unsigned char*>(bm[i].bmBits);

// Play with buf[i]
// ...

pic[i].SetBitmap(hbm[i]);

My program rotates the picture when user clicks on it an moves his mouse.

Why does it flicker even though there is only one thread in my MFC application? Theoretically there is no chance of parallel access. How does double buffering then solve this problem?

Thanks
Kaushik SV