I modified application/views/register/registerForm.php to revert to prior behavior, although this should I suppose be configurable for those who don't want or need to require first and last names for new tokens.

<label for='register_firstname' class='control-label col-md-4'><span class="text-danger asterisk"></span> <?php eT("First name:"); ?></label>
<div class="col-sm-12 col-md-6">
    <?php echo CHtml::textField('register_firstname', $sFirstName,array('id'=>'register_firstname','class'=>'form-control input-sm','required'=>'required')); ?>
</div>

</div>
<div class='form-group col-sm-12'>
<label for='register_lastname' class='control-label col-md-4'><span class="text-danger asterisk"></span> <?php eT("Last name:"); ?></label>
<div class="col-sm-12 col-md-6">
<?php echo CHtml::textField('register_lastname', $sLastName,array('id'=>'register_lastname','class'=>'form-control input-sm','required'=>'required')); ?>
</div>