display list empty despite presence of display object

assuming _context is mainTimeLine and we have an mc called 'test_mc' there at frame 20 (as in, starting at 20, so not on frame 19), this would be fine in AS2 but just produces a 'null' result in AS3:

class someClass{

public method someMethod()
{
_context.gotoAndStop(20);
trace(_context.test_mc);
}
}

what's the craic there then? :)

dub.