Update commands are by default sent to the active view only. Try adding the following to CMainFrame to change this routing:

Code:
BOOL CMainFrame::OnCmdMsg(UINT nID, int nCode, void* pExtra, AFX_CMDHANDLERINFO* pHandlerInfo) 
{
    CDocument *pDoc = GetActiveDocument();
    if(pDoc)
    {
	POSITION pos = pDoc->GetFirstViewPosition();
	CView *pView = NULL;
	while(pView = pDoc->GetNextView(pos))
	{
	    if(pView != GetActiveView()
		&& pView->OnCmdMsg(nID, nCode, pExtra, pHandlerInfo))
		return TRUE;
	}
    }

    return CFrameWnd::OnCmdMsg(nID, nCode, pExtra, pHandlerInfo);
}