Small problem, first the function $this->ion_auth->is_group($group) should be in_group().
I think I remember seeing this elsewhere. However a problem exists if you pass an array of groups.
Currently is_group returns in_array($check_group, $groups) which won't work if check_group is an array.
Solution:
application/libraries/Icon_auth.php
Add condition to check if $check_groups is an array and if it is then walk through the array checking for a match.
Code:
public function in_group($check_group)
{
$this->ci->ion_auth_model->trigger_events('is_group');