CToolTipCtrl tooltip do not reappear second time on CBitmapButton Control

I have VS2010 Project which is an MFC dialog application which uses CToolTipCtrl for implementing tooltip on a CBitmapButton control. I have observed that when I hover my mouse for the first time on the CBitmapButton control, tooltip appears and after the time expires tooltip disappears. when I hover my mouse again on the same control tooltip never appears. I have attached my code here

------------CBitmapButtonWithTooltip.cpp--------------------

#include "stdafx.h"

#include "CBitmapButtonWithTooltip.h"
void CBitmapButtonWithTooltip::CreateToolTip(){    

    m_tt.Create(this, TTS_ALWAYSTIP);
    m_tt.SetDelayTime(TTDT_AUTOPOP, 10000);            // The time that the tip shows    
    m_tt.SetDelayTime(TTDT_INITIAL, 100);              // The delay before the tip shows
    m_tt.Activate(TRUE);    
    m_tt.AddTool(this, _T("ToolTip test with Cbitmap button"));
}

BOOL CBitmapButtonWithTooltip::PreTranslateMessage(MSG* pMsg)
{
    if (pMsg->message >= WM_MOUSEFIRST && pMsg->message <= WM_MOUSELAST)
        m_tt.RelayEvent(pMsg);

    return CBitmapButton::PreTranslateMessage(pMsg);
}

------------CBitmapButtonWithTooltip.h--------------------

class CICBitmapButtonWithTooltip : public CBitmapButton 
{
public:
    CToolTipCtrl m_tt;
    CICBitmapButtonWithTooltip(CWnd* pParent = NULL);
    ~CICBitmapButtonWithTooltip();

    void CreateToolTip();    
    BOOL PreTranslateMessage(MSG* pMsg);    
    DECLARE_MESSAGE_MAP()
};

I create an object and use as follows

   CICBitmapButtonWithTooltip m_bButtonTip; 
    m_bButtonTip.Create(NULL,  WS_CHILD |BS_OWNERDRAW, CRect(0, 0, 48, 48), this, NULL);
    m_bButtonTip.LoadBitmaps(IDB_BITMAP1);
    m_bButtonTip.SetWindowPos(NULL, 50, 50, 48, 48, SWP_HIDEWINDOW);
    m_bButtonTip.ShowWindow(SW_SHOW);
    m_bButtonTip.CreateToolTip();