Blur Event not fired after Date Picking

[It_Barney]

    public void onModuleLoad() {
        final DateField df = new DateField();
        TextButton tb = new TextButton("Test");
        tb.addSelectHandler(new SelectHandler() {
            public void onSelect(SelectEvent event) {
                System.out.println(df.getValue());
            }
        });
        RootPanel.get().add(df);
        RootPanel.get().add(tb);
    }

Steps to reproduce the problem:
- Pick a Date by the DatePicker
- Click directly on the TextButton

Steps for correct behaving:
- Pick a Date by the DatePicker
- Use Tab key to move focus from the DateField to the TextButton
- Click the TextButton

Thanks in advance