A question about thread,please help me

 My program environment is .net2005.The partial code is shown as below:
     void CfinalView::OnRButtonDblClk(UINT nFlags, CPoint point)
     {
     CRect rc;
     GetClientRect(&rc);
     
if(point.x>rc.left&&point.x<(rc.right/2)&&point.y>rc.top&&point.y<rc.bottom)
     {
         //AfxBeginThread(RUNTIME_CLASS(CDetailPlot));
     }
     
if(point.x>(rc.right/2)&&point.x<rc.right&&point.y>rc.top&&point.y<(rc.bottom/2))
     {
         //AfxMessageBox(_T("haha"));
         AfxBeginThread(RUNTIME_CLASS(CDetailPlot));
     }
     CView::OnRButtonDblClk(nFlags, point);
 }
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 BOOL CDetailPlot::InitInstance()
 {
     pCFrameWnd=new CMyFrameWnd();
     pCFrameWnd->Create(NULL,_T("6?_5T?5:U"));
     HWND hWnd=pCFrameWnd->GetSafeHwnd();
     pCFrameWnd->ShowWindow(SW_SHOW);
     ChidThread=AfxBeginThread(PlotConstell,(LPVOID)pCFrameWnd);
     pCFrameWnd->ChildThread=ChidThread;
     //Listen((LPVOID)pFrameWnd);
     return TRUE;
 }
----------------------------------------------------------------------------
 void CMyFrameWnd::OnLButtonUp(UINT nFlags, CPoint point)
 {
     DCount++;
     if(DCount%2!=0)
     {
         SuspendThread(ChildThread->m_hThread);
     }
     else
     {
         ResumeThread(ChildThread->m_hThread);
     }
     CFrameWnd::OnLButtonUp(nFlags, point);
 }
 ---------------------------------------------------------------------------
 class CMyFrameWnd : public CFrameWnd
 {
     DECLARE_DYNCREATE(CMyFrameWnd)
 public:
     CMyFrameWnd(); // 5
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     virtual ~CMyFrameWnd();
 protected:
     DECLARE_MESSAGE_MAP()
 public:
     afx_msg void OnLButtonUp(UINT nFlags, CPoint point);
     CWinThread *ChildThread;
 public:
     int DCount;
 };
   What I want to do is create a user-interface thread when double check the
left button of mouse in mainframe.And then in the new window I want to create
another worker thread to plot.When it plotting , I could suspend/resume the
plot thread by check left button.
    The problem is when the child-window responsed the mouse's
action(suspend plot thread) , it may suspend the thread of mainframe
stochastic, and another check will resume both of then.
     Please tell me why it happened and how to deal with.Thank you.