Why is my subclassed window not visible?

Question

I'm following mcdave's advice from http://stackoverflow.com/questions/2191637 and using SubclassWindpow to host a CIPAddressCtrl in a winforms app. My constructor looks like this:

IPAddressBox::IPAddressBox(void)
{
    // I have tried it with and without this part
    INITCOMMONCONTROLSEX icc;
    icc.dwICC = ICC_INTERNET_CLASSES;
    icc.dwSize = sizeof(INITCOMMONCONTROLSEX);
    ::InitCommonControlsEx(&icc);

    m_pCtrl = new CIPAddressCtrl();
}

and my OnHandleCreated function looks like this:

void IPAddressBox::OnHandleCreated(EventArgs^ e)
{
    if (m_pCtrl->GetSafeHwnd() != NULL)
        throw gcnew InvalidOperationException("Cannot create handle; MFC control already has an HWND");

    if (!m_pCtrl->SubclassWindow((HWND)this->Handle.ToPointer()))
        throw gcnew InvalidOperationException("Could not attach MFC control");

    Control::OnHandleCreated(e);
}

When my winforms control is shown on screen, nothing happens - the control's BackColor shows and I don't see a CIPAddressCtrl.

What do I need to do to get the CIPAddressCtrl to draw itself on the screen?