When adding a new bound property through the GUI, no property change event will ever be thrown.

If you use ALT+INSERT > "add Property ... " to add a bound property X, it will generate this setter

public void setX(String X) {
        String oldX = X;
        this.X = X;
        propertySupport.firePropertyChange(PROP_X, oldX, X);
    }

Note that this always sets oldX = X, so no property change event is ever thrown.

The correct code for line 2 would be:

        String oldX = this.X;