why StretchBlt allocated two times memory in windows 2003 than xp?

void GetEmfByBytes(BYTE * pBits, int iWidth, int iHeight, WCHAR* szPrinterName, WCHAR* szDestinationFile,DWORD rop=SRCCOPY)
{
    BITMAP bm;

    HDC hdcMem = CreateCompatibleDC(GetDC(NULL));
    HDC hPrinterDC = ::CreateDC(NULL,szPrinterName, NULL, NULL);

    BITMAPINFOHEADER bmih;
    memset(&bmih, 0, sizeof(BITMAPINFOHEADER));

    bmih.biSize = sizeof(BITMAPINFOHEADER);
    bmih.biBitCount = 1;
    bmih.biCompression = BI_RGB;
    bmih.biPlanes = 1;
    bmih.biWidth = iWidth;
    bmih.biHeight = iHeight;

    BITMAPINFO bmi;
    memset(&bmi, 0, sizeof(BITMAPINFO));

    bmi.bmiHeader = bmih;

    HBITMAP hBmp = ::CreateDIBitmap(hPrinterDC,&bmih,CBM_INIT,pBits,&bmi,0);

    GetObject(hBmp, sizeof(BITMAP), &bm );
    SelectObject(hdcMem, hBmp);
    HDC emfdc = CreateEnhMetaFile(hPrinterDC, szDestinationFile, NULL, L"");

    if(emfdc!=NULL){
        StretchBlt(emfdc,0, 0, bm.bmWidth, -bm.bmHeight, hdcMem, 0, 0, bm.bmWidth, bm.bmHeight, rop);// From task     manager I found the memory of spoolsv.exe increased 
        // 4M in xp, while 8M in windows 2003.
        //DeleteDC(emfdc);
        HENHMETAFILE hEMFFile = CloseEnhMetaFile(emfdc);// 4M memory were released in both xp and windows 2003. So     4M memory were still not released in windows 2003. Memory Leak!
        DeleteEnhMetaFile(hEMFFile);
        //DeleteDC(emfdc);
    }else{
        logOut( wstring(L"can't create emf")+szDestinationFile );
    }

    DeleteDC(hPrinterDC);
    DeleteDC(hdcMem);
    DeleteObject(hBmp);
}