GUI Builder: unable to access components via bound class

I have a Swing form with a bound Java class created in the GUI builder.

The form and its listeners are running fine. It's initialised from a class outside the form:

form = new TradeManagerForm();
form.setStrategy(this);

JFrame panel = new JFrame("Trade Manager");
panel.setContentPane(form.getMainPanel());
panel.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
panel.pack();
panel.setVisible(true);

The builder has added all the form components as class properties in the bound class. According to the docs, I should be able to add runtime functionality to the form via these class properties:

https://www.jetbrains.com/help/idea/2016.1/bound-class.html

I've set up accessors within the bound class so the app can interact with the form (eg, enable/disable buttons), but none of them work. When called, nothing changes on the form and no error is thrown. Here's an example accessor:

public void testForm(){

labelFoo.setText("Test value!");
labelFoo.setForeground(Color.RED);
buttonFoo.setEnabled(false);
}

I've tried calling repaint() on the component after each change but it hasn't helped. It shouldn't be required anyway, as I understand it.

I'm a Swing and IDEA newbie, so am probably doing something dim. Please help - this is a show-stopper for my project.