Inconsisten behaviour in User admin display

[Filip Gruszczyński]

I needed to change admin site for User class from auth, because I need to make first name and last name required. I subclassed Admin class for User and changed form:

class UserChangeForm(ModelForm):

username = RegexField(label=_("Username"), max_length=30, regex=r'^\w+$',

help_text = _("Required. 30 characters or fewer. Alphanumeric characters only (letters, digits and underscores)."),
error_message = _("This value must contain only letters, numbers and underscores."))

first_name = CharField(label=_('first name'), max_length=30, required=True)
last_name = CharField(label=_('last name'), max_length=30, required=True)

class Meta:

model = User

Without first_name and last_name fields defined, admin displays it translated into polish, with first letter capitalized, like this:

Imie
Nazwiski

With first_name and last_name fields defined, which have labels defined exactly as User model ('first name' and 'last name'), admin displays it translated, but not capitalized, like this:

imie
nazwisko

The other labels are capitalized and I would like to be consistent. Is there any way to make it consistent?