Demo: TextField.text behaves differently when a stylesheet is set, even if the stylesheet is empty. The desired behavior is to get styled plain text (i.e. literal <i> tags displayed in output).

HelloWorld.as

package {
    import flash.text.TextField;
    import flash.text.StyleSheet;

    import flash.display.Sprite;
    import flash.system.Capabilities;

    public class HelloWorld extends Sprite {
        private var textField:TextField;

        public function HelloWorld( ) {
            graphics.beginFill( 0xFFCC00 );
            graphics.drawCircle( 40, 40, 40 );
            trace("Hello, world!");
            trace("isDebugger", Capabilities.isDebugger);
            trace("isDebugBuild", (new Error().getStackTrace().search(/:[0-9]+]$/m) > -1));

            this.textField = new TextField();

            this.stage.addChild(this.textField);

            var style:StyleSheet = new StyleSheet();
            //style.parseCSS('* { color: #7e1e9c; size: 15px; font-weight: bold; font-family: arial; }')
            this.textField.styleSheet = style;

            this.textField.text = '<i>test</i>';
        }
    }
}