form_hidden bug

The code below generates duplicate hidden inputs. Because third arg ('id="old_email"') in third row of code is an extra and it is added mistakenly. But this results in duplicate hidden inputs. So is this a bug?

Code:
<?php echo form_open('/user/edit', 'class="form"'); ?>
<?php echo form_hidden('id', '3'); ?>
<?php echo form_hidden('old_email', '[email protected]', 'id="old_email"'); ?>
<?php echo form_submit('submit', 'Submit'); ?>
<?php echo form_close(); ?>

Print:
<form action="/user/edit" class="form" method="post" accept-charset="utf-8">
<input type="hidden" name="id" value="3">
<input type="hidden" name="id" value="3">
<input type="hidden" name="old_email" value="[email protected]">
<input type="submit" name="submit" value="Submit">
</form>