GUIRegisterMsg not working

#include
#include
#include


GUIRegisterMsg($WM_NCHITTEST, "WM_NCHITTEST")

$hGUI = GUICreate("Test", 500, 200, -1, 100)
$caption = GUICtrlCreateLabel("example", 200, 100, 150, 26)
$iBtn_Exit = GUICtrlCreateButton("Exit", 200, 150, 100, 40)
;~ GUISetState()
$hGUI2 = GUICreate("gui2", 150, 70, 10, 10, $WS_POPUP, $WS_EX_MDICHILD, $hGUI)
$iBtn_Effect2 = GUICtrlCreateButton("XXXX", 10, 10, 100, 40)
GUISetBkColor(0xE0FFFF, $hGUI2)

$hGUI3 = GUICreate("gui3", 150, 70, 10, 80, $WS_POPUP, $WS_EX_MDICHILD, $hGUI)
GUISetBkColor(0xA0FFFF, $hGUI3)
$img = GUICtrlCreatePic("mslogo.jpg", 10, 10, 100, 50)

GUISetState(@SW_SHOW, $hGUI)
GUISetState(@SW_SHOW, $hGUI2)
GUISetState(@SW_SHOW, $hGUI3)

Global $hHBmp
Do
Switch GUIGetMsg()
Case $GUI_EVENT_CLOSE, $iBtn_Exit
GUIDelete()
Exit

EndSwitch
Until False

Func WM_NCHITTEST($hWnd, $iMsg, $iwParam, $ilParam)
GUICtrlSetData($caption, $hWnd & " " & Random()) ; for test
If (($hwnd = $hGUI) or ($hwnd = $hGUI2) or ($hwnd = $hGUI3)) And ($iMsg = $WM_NCHITTEST) Then
_SendMessage($hGUI,$WM_SYSCOMMAND,0xF012,0)
EndIf
EndFunc