GetSel method always returns zero on CEdit control

Question

On a MFC application a CEdit control of a dialogue is subclassed. There is a numerical keypad on another dialogue which is supposed to send values to that text box. If the text is highlighted on the edit control the GetSel method returns the start and end index of the highlighted text and this will be replaced with the value comes from the keypad. This works fine.

Now if the the subclassed CEdit become a part of a custom CComboBox control the GetSel method on the CEdit control of combobox always returns 0.

I don't seem to realize what the reason and solution is. And would appreciate any help. Thanks.

Update:

Here is the piece of code that tries to get the highlighted text

BOOL CBaseDialog::PreTranslateMessage(MSG* pMsg) 
{
    if (pMsg->message == WM_KEYDOWN && pMsg->lParam == 2)
    {
        switch (pMsg->wParam)
        {
            case VK_TAB:
                //NextDialogCtrl();
                break;
            case 'ret':
                //keybd_event(VK_RETURN, 0, 0, 0);
                return FALSE;
            case '?':
                break;
            default:
                if (m_LastFocused >= 0)
                {        
                    CWnd* pwnd = GetDlgItem(m_LastFocused);

                    if (pwnd->IsKindOf(RUNTIME_CLASS(CComboBox)) )
                    {
                        CCustomComboBox* ctl = (CCustomComboBox*)pwnd;  

                        //this method always returns 0 index for the 
                        //start and end position index
                        ctl->m_edit->GetSel(m_LastStPos, m_LastEndPos);
                    }
                }
        } break;
    }
}

The combo is subclassed like this:

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

    //combo is CCustomComboBox type
    combo.SubclassDlgItem(IDC_COMBO,this);

   //rest of the code...
}

And the CEdit control:

HBRUSH CCustomComboBox::OnCtlColor(CDC* pDC, CWnd* pWnd, UINT nCtlColor)
{
    if (nCtlColor == CTLCOLOR_EDIT)
    {
        //[ASCII 160][ASCII 160][ASCII 160]Edit control
        if (m_edit.GetSafeHwnd() == NULL)
            m_edit.SubclassWindow(pWnd->GetSafeHwnd());
    }
    else if (nCtlColor == CTLCOLOR_LISTBOX)
    {
        //ListBox control
        if (m_listbox.GetSafeHwnd() == NULL)
            m_listbox.SubclassWindow(pWnd->GetSafeHwnd());
    }
    HBRUSH hbr = CComboBox::OnCtlColor(pDC, pWnd, nCtlColor);
    return hbr;
}