title: Why a child window may not receive mouse events?
body: <p>I have a custom WTL control which is a panel with a list and a custom scroll bar.</p>
  
  <pre><code>class Panel
  : public ATL::CWindowImpl&lt;Panel&gt;, public WTL::CDoubleBufferImpl&lt;Panel&gt; {
  public:
      DECLARE_WND_CLASS("Panel")
  
      BEGIN_MSG_MAP_EX(Panel)
          MSG_WM_CREATE(OnCreate)
          MSG_WM_DESTROY(OnDestroy)
          MSG_WM_SIZE(OnSize)
          CHAIN_MSG_MAP(CDoubleBufferImpl&lt;Panel&gt;)
          REFLECT_NOTIFICATIONS()
      END_MSG_MAP()
  </code></pre>
  
  <p>The scroll bar is created by the panel in OnCreate():</p>
  
  <pre><code>m_scrollBar.Create(m_hWnd, WTL::CRect(...));
  </code></pre>
  
  <p>That scroll bar works fine in many other dialog windows. However, inside that panel control the scroll bar appears, but receives no mouse events at all. If I add <code>WM_MOUSEMOVE</code> handler to the panel, it does get called.</p>
  
  <p>What could be the problem?</p>