视频捕捉的窗口为什么会浮起来？

以下是我的代码：
HRESULT InitCaptureGraph()
{
    HRESULT hr;    // get whatever capture device exists
    //
    JIF(CoCreateInstance(CLSID_FilterGraph, NULL, CLSCTX_INPROC_SERVER, 
                         IID_IGraphBuilder, (void **)&pGB));
    CComPtr< IBaseFilter > pCap;
    GetDefaultCapDevice( &pCap );
    if( !pCap )
    {
        Msg(TEXT( "No video capture device was detected on your system.\r\n\r\n"
               "This sample requires a functional video capture device, such\r\n"
               "as a USB web camera." ));
        return E_FAIL;
    }    // add the capture filter to the graph
    //
    hr = pGB->AddFilter( pCap, L"Cap" );
    if( FAILED( hr ) )
    {
        Msg(TEXT( "Could not put capture device in graph" ));
        return hr;
    }    // make a capture builder graph (for connecting help)
    //
    CComPtr< ICaptureGraphBuilder2 > pBuilder;
    hr = pBuilder.CoCreateInstance( CLSID_CaptureGraphBuilder2 );
    if( !pBuilder )
    {
        Msg(TEXT( "Could not create capture graph builder2" ));
        return hr;
    }    hr = pBuilder->SetFiltergraph( pGB );
    if( FAILED( hr ) )
    {
        Msg(TEXT( "Could not set filtergraph on graphbuilder2" ));
        return hr;
    }    CComPtr< IBaseFilter > pMux;
    CComPtr< IFileSinkFilter > pSink;
    USES_CONVERSION;    hr = pBuilder->RenderStream( &PIN_CATEGORY_CAPTURE,
        &MEDIATYPE_Video,
        pCap,
        NULL,
        pMux );
    if( FAILED( hr ) )
    {
        Msg(TEXT( "Could not connect capture pin" ));
        return hr;
    }    hr = pBuilder->RenderStream( &PIN_CATEGORY_PREVIEW,
        &MEDIATYPE_Video,
        pCap,
        NULL,
        NULL );
    if( FAILED( hr ) )
    {
        Msg(TEXT("Could not render capture pin" ));
        return hr;
    }
    if( hr == VFW_S_NOPREVIEWPIN )
    {
        // preview was faked up using the capture pin, so we can't
        // turn capture on and off at will.
        hr = 0;
    }    // find the video window and stuff it in our window
    //
    CComQIPtr< IVideoWindow, &IID_IVideoWindow > pWindow = pGB;
    if( !pWindow )
    {
        Msg(TEXT("Could not get video window interface" ));
        return hr;
    }    // set up the preview window to be in our dialog
    // instead of floating popup
    //
    if (SUCCEEDED(pWindow->put_Owner(  (OAHWND)ghApp )))
{
    pWindow->put_Left( 0 );
    pWindow->put_Top( 0 );
    pWindow->put_Width( 320 );
    pWindow->put_Height( 240 );
    pWindow->put_Visible( OATRUE );
    pWindow->put_WindowStyle( WS_CHILD | WS_CLIPSIBLINGS );
}
    // run the graph
    //
    CComQIPtr< IMediaControl, &IID_IMediaControl > pControl = pGB;
    hr = pControl->Run( );
    if( FAILED( hr ) )
    {
        Msg(TEXT("Could not run graph" ));
        return hr;
    }    
    return 0;
}已经put_Owner了为什么还会浮起来呢？是不是跟owner的窗口有关系呢？我的窗口是这样生成的
    ghApp = CreateWindow(CLASSNAME, APPLICATIONNAME,
                         WS_OVERLAPPEDWINDOW | WS_CAPTION | WS_CLIPCHILDREN | WS_VISIBLE,
                         CW_USEDEFAULT, CW_USEDEFAULT,
                         DEFAULT_PLAYER_WIDTH, DEFAULT_PLAYER_HEIGHT,
                         0, 0, ghInst, 0);