What’s wrong with this code part 24 (From an MSDN article)?

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I ran into this bug earlier today and realized that it’d make an awesome “What’s wrong with this code”.

I started pulling together a test app when I realized that this MSDN magazine article contains sample code that perfectly exhibits the bug:

 CRect rectangle;
VERIFY(m_splitButton.GetWindowRect(
    &rectangle));

TPMPARAMS params = { sizeof(TPMPARAMS) };
params.rcExclude = rectangle;

CMenuHandle menu = m_menu.GetSubMenu(0);

VERIFY(menu.TrackPopupMenuEx(TPM_LEFTBUTTON,
    rectangle.left, rectangle.bottom,
    m_hWnd, &params));

There’s not much to the code – it’s from the handler for the BCN_DROPDOWN notification message.  And it’s got a very nasty subtle bug in it.

So what’s the bug?

 

Edit: s/nasty/subtle/