[fljot]

public static function fixHeight(textfield:TextField):void
{
	textfield.autoSize = TextFieldAutoSize.LEFT;
	var h:Number = textfield.height;
	textfield.autoSize = TextFieldAutoSize.NONE;
	// adding extra height will prevent "vertical scroll on text select" bug
	// the extra height value should be just bigger than the default leading
	textfield.height = h + Number(textfield.getTextFormat().leading) + 1;
}

Будет работать, только если одна высота строк.