Detecting if there is a timeline mask

I am bumping into a very strange behaviour on Flash. If you on the Flash IDE create a shape with a mask associated to it, save it and then export it as a swf, you cannot programatically know there is a mask (displayObject.mask is null)

Here's a simple test script to prove that:

//executed on enter_frame with the root object
function test(d:DisplayObject) : Void
{
    if (Std.is(d, DisplayObjectContainer))
    {
        var s:DisplayObjectContainer =  cast d;
        for (i in 0...s.numChildren)
            test(s.getChildAt(i));
    }

    if (d.mask != null)
        trace("FOUND " + d.name);
}

The syntax is a little different since it's haxe, but 开发者_如何学编程it will display the same on vanilla AS3

traces that no mask was found! I just need to handle differently the cases where there is a mask attached to it, so is there any way/workaround this strange issue?

Pretty sure this is impossible... and here is a thread to back me up:

http://www.actionscript.org/forums/archive/index.php3/t-184762.html