Problema cancelando método doinbackground

public class VygerGUI extends javax.swing.JFrame {
//...
private static Executar exec;
//declaracoes
public VygerGUI() {
init components;
//...
}
protected class Executar extends SwingWorker<Void, Void> {

            @Override
            public Void doInBackground() throws Exception {
//...
//faço tudo... (usando outras classes)
        }
}

//aí tem os métodos que o netbeans mesmo cria pra tratar eventos

    private void jButtonCalcularMouseClicked(java.awt.event.MouseEvent evt) {                                             
        // TODO add your handling code here:
        jButtonAbortar.setVisible(true);
        exec = new Executar();
        try {
            exec.execute();
        } catch (Exception ex) {
            Logger.getLogger(VygerGUI.class.getName()).log(Level.SEVERE, null, ex);
        }
    } 

private void jButtonAbortar1MouseClicked(java.awt.event.MouseEvent evt) {                                             
            // TODO add your handling code here:
            exec.cancel(true);
            jButtonAbortar1.setVisible(false);
            if(exec.isCancelled()) System.out.println("Cancelou!!");
        }   
public static void main(String args[]) {
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                new VygerGUI().setVisible(true);
            }
        });
    }
//...
// algumas declarações de componentes da GUI
}