Steps to reproduce the issue

Create a form field:

<field
   name="myfield"
   type="usergroup"
   label="User Group">
   <option value="">No Group</option>
</field>

Expected result

A dropdown with 'No Group' as the initially selected value.

Actual result

A dropdown with 'Show All Groups' as the initially selected value

System information (as much as possible)

JFormFieldUsergroup::getInput() returns with:

return JHtml::_('access.usergroup', $this->name, $this->value, $attr, $options, $this->id);

But the class is defined as:

JHtmlAccess::usergroup($name, $selected, $attribs = '', $allowAll = true)

Note that $options is being passed to $allowAll. On a slightly related note, the call is passing a fifth argument the method doesn't accept at all.

In addition, there is another form field JFormFieldUsergrouplist which does work as expected. It would seem both form fields are intended to serve the same function and so are duplicates. JFormFieldUsergroup should either be fixed or deprecated.

Additional comments

I have a plugin in which I want to have a user group optionally selected. Since it isn't required, JFormFieldUsergroup won't work. JFormFieldUsergrouplist does exactly what I need.