[C#] SendMessageでCheckBoxのBM_GETCHECKの戻り値が旨く取得できません

        /// <summary>
        /// Gets the toggle state of an element in the target application.
        /// </summary>
        /// <param name="element">The target element.</param>
        private bool IsElementToggledOn(AutomationElement element)
        {
            if (element == null)
            {
                // TODO: Invalid parameter error handling.
                return false;
            }

            Object objPattern;
            TogglePattern togPattern;
            if (true == element.TryGetCurrentPattern(TogglePattern.Pattern, out objPattern))
            {
                togPattern = objPattern as TogglePattern;
                return togPattern.Current.ToggleState == ToggleState.On;
            }
            // TODO: Object doesn't support TogglePattern error handling.
            return false;
        }



        private void button7_Click(object sender, EventArgs e)
        {
            hWndc = new IntPtr(0x000A059C);// 取りあえずダイレクトにハンドルを指定

            AutomationElement AutoEle = AutomationElement.FromHandle(hWndc);
            bool ss = IsElementToggledOn(AutoEle);
            checkBox1.Checked = ss;
        }

[DllImport("oleacc.dll", PreserveSig = false)]
[return: MarshalAs(UnmanagedType.Interface)]
public static extern object AccessibleObjectFromWindow(IntPtr hwnd, uint dwId, ref Guid riid);

const UInt32 OBJID_CLIENT = 0xFFFFFFFC;
const int UNCHECKED = 1048576;
const int CHECKED = 1048592;
Guid uid = new Guid("618736e0-3c3d-11cf-810c-00aa00389b71");

private void button4_Click(object sender, EventArgs e)
{
    Accessibility.IAccessible accObj = (Accessibility.IAccessible)AccessibleObjectFromWindow(hWndc, OBJID_CLIENT, ref uid);
    int state = (int)accObj.get_accState(0);
    switch (state)
    {
        case UNCHECKED:
            textBox5.Text = "UNCHECKED";
            break;
        case CHECKED:
            textBox5.Text = "CHECKED";
            break;
        default:
            textBox5.Text = "UNKNOWN";
            break;
    }
}

private static extern IntPtr SendMessage(IntPtr hWnd, uint Msg, IntPtr wParam, IntPtr lParam);