extending the ports

Dear all,
    I have developed a set of nodes for sql executions. The port of my nodes use an extension of DatabasePortObject defined as:

public class MyDatabasePortObject extends DatabasePortObject{

    CredentialsProvider cp;
    public static final PortType TYPE = new PortType(MyDatabasePortObject.

    public MyDatabasePortObject(DatabasePortObjectSpec spec) {
            this(spec, null);
    public MyDatabasePortObject(DatabasePortObjectSpec spec, CredentialsProvider credentials) {
        cp = credentials;
    public JComponent[] getViews() {


The constructor of my node models are defined as follows:

public class MyNodeModel extends DBNodeModel {

    protected MyNodeModel(){
        super( new PortType[]{DatabasePortObject.TYPE},
                   new PortType[]{MyDatabasePortObject.TYPE});



When executed workflows are re-opened, its node status are modified from "EXECUTED" to "CONFIGURED" due to inconsistency on the port objects.
For the same reason, in the KNIME server the workflows cannot be executed.
What is wrong in my definitions? How can I configure the appereance of my portobject?

Thank you very much in advance,