When an instance of ComboBox is created in the ComboBoxTableCell.startEdit() method the converter that was assigned to the ComboBoxTableCell is not passed on to the ComboBox instance. Consequently the default toString() method is called on the items when the drop down is rendered. The method should look like this:

    @Override public void startEdit() {
..........
        if (comboBox == null) {
            comboBox = createComboBox(this, items);
            comboBox.setConverter(getConverter()); <-------- to be added
            comboBox.editableProperty().bind(comboBoxEditableProperty());
        }
.........