为什么响应消息WM_MOUSELEAVE而不响应消息WM_MOUSEHOVER

以下是程序的代码：
头文件-------------------------------------------------------------------------------
class CMyButton :public CButton
{
public:
CMyButton(void);
~CMyButton(void);
LRESULT OnMouseLeave(WPARAM wParam,LPARAM lParam);
LRESULT OnMouseHover(WPARAM wParam,LPARAM lParam);
protected:
bool m_bTracked;
DECLARE_MESSAGE_MAP()
afx_msg void OnMouseMove(UINT nFlags, CPoint point);
};

源文件-----------------------------------------------------------------------------
#include "StdAfx.h"
#include "MyButton.h"


CMyButton::CMyButton(void)
{
m_bTracked=true;
}


CMyButton::~CMyButton(void)
{
}
BEGIN_MESSAGE_MAP(CMyButton, CButton)
ON_WM_MOUSEMOVE()
ON_MESSAGE(WM_MOUSEHOVER,OnMouseHover)
ON_MESSAGE(WM_MOUSELEAVE,OnMouseLeave)
END_MESSAGE_MAP()


void CMyButton::OnMouseMove(UINT nFlags, CPoint point)
{
if(m_bTracked){
TRACKMOUSEEVENT tme;
ZeroMemory(&tme,sizeof(TRACKMOUSEEVENT));
tme.cbSize=sizeof(TRACKMOUSEEVENT)+1;
tme.dwFlags=TME_HOVER|TME_LEAVE;
tme.dwHoverTime=1; //鼠标在按钮上停留超过1s,就认为是HOVER
tme.hwndTrack=this->m_hWnd;
if(::_TrackMouseEvent(&tme))
m_bTracked=false;
}
CButton::OnMouseMove(nFlags, point);
}
LRESULT CMyButton::OnMouseLeave(WPARAM wParam,LPARAM lParam)
{
RedrawWindow();
TRACE(_T("Leave---------------------------"));
m_bTracked=true;
return 0;
}
LRESULT CMyButton::OnMouseHover(WPARAM wParam,LPARAM lParam)
{
RedrawWindow();
TRACE(_T("Hover---------------------------"));
m_bTracked=false;
return 0;
}


求各位大侠指点？