Option button unselects itself when i click a command button

How do I keep this from happening? I think it might be causing another bug where the program just displays default settings.

Code:

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void CTestAppDlg::OnSelectpizzasize()
{       
        switch (m_intPizzaSize)
        {
        case 0:
                m_strOrderInfo = "Small Pizza";
                break;
        case 1:
                m_strOrderInfo = "Medium Pizza";
                break;
        case 2:
                m_strOrderInfo = "Large Pizza";
                break;
        default:
                m_strOrderInfo = "Test";
                break;
        }

        UpdateData(FALSE);
}

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