[fw-mvc] "fieldset-" prepended to Zend_Form display group name?

Hi,

I just updated my current project to 1.6 and noticed that the id of the
fieldset now has the text "fieldset-" prepended to the name I assign to
the display group:

For example, in my form I have:

$this->addDisplayGroup($displayGroupArray,
'contactUsForm',
array(
'legend' => 'Contact Form',
)
);

which now outputs:

<fieldset id="fieldset-contactUsForm"><legend>Contact Form</legend>...</fieldset>

Using 1.5.3 the id would only be id="contactUsForm". Bug?

Thanks,
Jeremy