src/main/java/org/efaps/ui/wicket/components/date/DateTimePanel.java
@Override
    protected void onAfterRender()
    {
        super.onAfterRender();
        final IDateListener container = this.findParent(IDateListener.class);
        if (container != null) {
            container.addDateComponent(this);
        }
    }
@Override
    protected void onAfterRender()
    {
        super.onAfterRender();
        final IDateListener container = this.findParent(IDateListener.class);
        if (container != null) {
            container.addDateComponent(this);
        }
    }
After rendering the datefields are added to the parent.