modal property not bindable in PopUp library ?

Hi,

I have the following declaration:

    <popup:PopUpWrapper
        modal="{pm && pm.progressBarModal}"
        open="{pm && pm.progressBarVisible}">

        <controls:ProgressControlBar
                progressBarMessage="{pm && pm.progressBarMessage}">
        </controls:ProgressControlBar>

    </popup:PopUpWrapper>

While open binds nicely to my pm, modal refuses.

I have checked the library implementation, and I see that modal is declared as [Bindable]

  [Bindable(event="propertyChange")]
  native public function get modal():Boolean;

  native public function set modal(value:Boolean):void;