The TYPE_MENUBUTTON constant allows the focus to travel from the button when the mouse is down, TYPE_PUSHBUTTON does not allow the focus to travel when the mouse is down.
The swf_startbutton() function starts off the definition of a button. The type parameter can either be TYPE_MENUBUTTON or TYPE_PUSHBUTTON. The TYPE_MENUBUTTON constant allows the focus to travel from the button when the mouse is down, TYPE_PUSHBUTTON does not allow the focus to travel when the mouse is down.