Q:

CView as tab on CMFCTabCtrl, does not draw invalidated area (on dragging)

I have a CWinAppEx MDI application, VS2017. The ChiledFrame is covered with (I altered the names for this question) CMyView:
pDocTemplate = new CMultiDocTemplate(   IDR_MYTYPE,
                                        RUNTIME_CLASS(CMyDoc),
                                        RUNTIME_CLASS(CMyChildFrame),
                                        RUNTIME_CLASS(CMyView));

CMyView client-rect is covered with a CMFCTabCtrl (m_wndTabs): It has 2 tabs, objects of CViewTest1 and CViewTest2 classes (derived from MFC CView). This is the relevant part of MyView::Create function:
    CRect rectDummy;
    rectDummy.SetRectEmpty();

    // Create tabs window:
    if (!m_wndTabs.Create(CMFCTabCtrl::STYLE_3D_ONENOTE, rectDummy, this, 1))
    {
        TRACE0("Failed to create output tab window\n");
        return -1;      // fail to create
    }

    // Create output panes ('300' value is dummy client-rect is updated on CViewTest1/2::OnSize):

    CViewTest1 *pWnd1 = (CViewTest1*)RUNTIME_CLASS(CViewTest1)->CreateObject();
    pWnd1->Create(nullptr, nullptr, LBS_NOINTEGRALHEIGHT | WS_CHILD | WS_VISIBLE, CRect(0, 0, 300, 300), this, 1, pContext);
    pWnd1->SetFont(&afxGlobalData.fontRegular);

    CViewTest2 *pWnd2 = (CViewTest2*)RUNTIME_CLASS(CViewTest2)->CreateObject();
    pWnd2->Create(nullptr, nullptr, LBS_NOINTEGRALHEIGHT | WS_CHILD | WS_VISIBLE, CRect(0, 0, 300, 300), this, 2, pContext);
    pWnd2->SetFont(&afxGlobalData.fontRegular);

    m_wndTabs.AddTab(pWnd1, L"Tab 1");
    m_wndTabs.AddTab(pWnd2, L"Tab 2");

    // Redraw tab 0 ("Tab 1"): <--- Here already smells an issue.
    m_wndTabs.SetActiveTab(1); // (This need to move to 1 & back to 0)
    m_wndTabs.SetActiveTab(0);

The parent of CViewTest1 and CViewTest2 objects is CMyView object.
m_wndTabs resized to cover the whole client area at:
void CMyView::OnSize(UINT nType, int cx, int cy)
{
    CView::OnSize(nType, cx, cy);

    if (m_wndTabs) // Tab control should cover the whole client area:
        m_wndTabs.SetWindowPos(nullptr, -1, -1, cx, cy, SWP_NOMOVE | SWP_NOACTIVATE | SWP_NOZORDER);

}

Now, when I drag one child-frame over another, and back: The control-tab behaves as expected, but CViewTest1 object (on active tab) does not get OnDraw(). It looks like that:

Any idea?

A:

CViewTest1 and 2 are CView classes. 
A CView should not contain other views. 
The outer frame should contain the Tab with the views.

