Leading wont work if autoSize is on

Anyone know why I cant apply leading to a text field if autoSize is on? I am using a new TextFormat and applying the leading after I autoSize…


....//some other code above you dont need to see
	var my_fmt:TextFormat = new TextFormat();
	mc.title.autoSize = true;
	mc.vidwin.subtitle.autoSize = true;
	my_fmt.leading = 2;
	mc.title.setTextFormat(my_fmt);