padnavigator demo generate QWindowsContext warnings

Start the padnavigator graphicsview example and then close it. It generates some warnings like this:

QWindowsContext::windowsProc: No Qt Window found for event 0x8 (WM_KILLFOCUS), hwnd=0x0x5ac0730.
QWindowsContext::windowsProc: No Qt Window found for event 0x6 (WM_ACTIVATE), hwnd=0x0x1d90764.
QWindowsContext::windowsProc: No Qt Window found for event 0x1c (WM_ACTIVATEAPP), hwnd=0x0x1d90764.
QWindowsContext::windowsProc: No Qt Window found for event 0x8 (WM_KILLFOCUS), hwnd=0x0x1d90764.