Problem with CComboboxEx / InsertItem...

Hi group;-)

Ive a little problem with a CComboboxEx-derived class and to check it,
i created a little test-dlg. i found that i have the same problem
without derivation and so ... here it is.

i have a dialog with a single CComboboxEx without imagelist (the
reference stated that i can can do this) and my system is VC6.

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class CTestDlg : public CDialog{
public:
    CTestDlg(CWnd* pParent = NULL); // standard constructor

    //{{AFX_DATA(CTestDlg)
    enum { IDD = IDD_TEST_DIALOG };
    CComboBoxEx m_Testcombo;
    //}}AFX_DATA

    //{{AFX_VIRTUAL(CTestDlg)
    protected:
    virtual void DoDataExchange(CDataExchange* pDX); // DDX/DDV support
    //}}AFX_VIRTUAL

protected:
    HICON m_hIcon;

    // Generated message map functions
    //{{AFX_MSG(CTestDlg)
    virtual BOOL OnInitDialog();
    afx_msg void OnPaint();
    afx_msg HCURSOR OnQueryDragIcon();
    //}}AFX_MSG
    DECLARE_MESSAGE_MAP()
};

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I do the following:

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BOOL CTestDlg::OnInitDialog(){
    CDialog::OnInitDialog();

    COMBOBOXEXITEM item;
    ZeroMemory(&item, sizeof(item));
    item.iItem = -1;
    item.pszText = _T("TEST");
    int iReturn = m_Testcombo.InsertItem(&item);

    return TRUE;
}

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i expected to have "TEST" in my Combo, but it stays emty.
iReturn is 0...?

Has anyone some enlightenment for me, please?