Why is Scripting.Dictionary.Add(hwnd) munging its reference?

#include <GUIConstantsEx.au3>
#include <WindowsConstants.au3>


global $gc_oForms=ObjCreate("Scripting.Dictionary")
global $make_error_happen=false
$make_error_happen=true

; Example shows destruction of hwnd by passing it to a dictionary object .Add, evidently by ref
; Is there something to know about handles and dictionaries?
;
Example1()


; example 1
Func Example1()
Local $msg
;
local $hGui=GUICreate("My GUI") ; will create a dialog box that when displayed is centered
;A valid hwnd
MsgBox(0,'Handle1',$hGui)
if $make_error_happen Then
     ;pass handle directly which will mung the $hGui variable up
     $gc_oForms.Add('stuff',$hGui)
     ;$hGui is invalid now, has been transformed - Autoit at fault or Dictionary?
     MsgBox(0,'Handle2',$hGui)
     MsgBox(0,'Handle3',$gc_oForms.Item('stuff'))
endif
local $cid=GUICtrlCreateButton("Darn Button",0,0)
;if $make_error_happen then this next call fails
local $p=ControlGetPos($hGui, "", $cid );xywh
if @error then
     MsgBox(0,"ERROR HERE",'@error:'&@error)
endif
;
GUISetState(@SW_SHOW) ; will display an empty dialog box

; Run the GUI until the dialog is closed
While 1
     $msg = GUIGetMsg()

     If $msg = $GUI_EVENT_CLOSE Then ExitLoop
WEnd
GUIDelete()
EndFunc ;==>Example1