New attribute created for PredictionModel subclass doesn't show up

Hi,

I am currently stuck with a quite simple problem. I have created a subclass of PredictionModel and modified the method createPredictionAttributes() as follows:

protected Attribute createPredictionAttributes(ExampleSet exampleSet, Attribute label) {
	// create and add prediction attribute

	/* make the label attribute independent from an existing label in the example set (since this had to be generated as dummy when classifying documents)
	 * original code:
	 * Attribute predictedLabel = AttributeFactory.createAttribute(label, Attributes.PREDICTION_NAME);
	 * predictedLabel.clearTransformations();
	*/

	Attribute predictedLabel = AttributeFactory.createAttribute(Attributes.PREDICTION_NAME, Ontology.NOMINAL);		

	ExampleTable table = exampleSet.getExampleTable();
	Attributes attributes = exampleSet.getAttributes();

	table.addAttribute(predictedLabel);
	attributes.setPredictedLabel(predictedLabel);

	// check whether confidence labels should be constructed
	if (supportsConfidences(predictedLabel)) {
		Iterator<String> labelIterator = model.classIndex.iterator();
		while (labelIterator.hasNext()) {
			String labelValue = labelIterator.next();
			Attribute confidence = AttributeFactory.createAttribute(Attributes.CONFIDENCE_NAME + "(" + labelValue + ")", Ontology.REAL);
			table.addAttribute(confidence);
			attributes.setSpecialAttribute(confidence, Attributes.CONFIDENCE_NAME + "_" + labelValue);
		}

		// create an additional attribute for the confidence of the predicted value
		Attribute predictionConfidence = AttributeFactory.createAttribute(Attributes.CONFIDENCE_NAME, Ontology.REAL);
		table.addAttribute(predictionConfidence);
		attributes.setSpecialAttribute(predictionConfidence, Attributes.CONFIDENCE_NAME);
	}

	return predictedLabel;
}

Creating the "confidence(...)" attributes works fine. After this I want to have an additional attribute "confidence" that holds the confidence of the value that was actually predicted. When printing the attribute to console I get the index of the attribute, which is the number of the existing attributes + 1. But the additional attribute doesn't show up in my example set after "Apply Model". I tried using different names or adding it as regular attribute. No chance...

I would be glad about any help with this.

Best regards
Matthias