The scrollbar is inactive!

When I use a code like this:

$hgui = GUICreate("title",800,650,-1,-1)
GUICtrlCreatePic("BilBoard.jpg", 0, 0, 800,600)
$Edit1 = GUICtrlCreateEdit("Some multiline text", 205, 145, 385, 245)
GUICtrlSetState($Edit1,$GUI_FOCUS)
GUISetState()
Do
Until GUIGetMsg() = $GUI_EVENT_CLOSE
GUIDelete($hgui)

the scrollbar is inactive. (I can not click on scrollbar to scroll the text down or up) but the mouse's wheel works.

and my "Some multiline text" is a 50lines text or more.