Strange problem in active records

[eluser]siptik[/eluser]
Hi all And sorry for my English.
Yesterday I had the strange problem:
It worked fine (bottom my code) but then I started getting the error.

Code:

function get_last_vacancies()
    {
    $this->db->select('*');
    $this->db->from('job_vacanсies');
    $this->db->join('job_specialty', 'job_vacanсies.v_specialty_id = job_specialty.specialty_id', 'left');
    return $this->db->get()->result_array();
    }

active record generate a wrong string:

SELECT * FROM (`job_vacanсies`) LEFT JOIN `job_specialty` ON `job_vacan`с`ies`.`v_specialty_id` = job_specialty.specialty_id

Have a look at `job_vacan`с`ies`.

Then I renamed the table name into "job_vac" and it started working fine.
Then I return the old name and it works fine again.

Question: How I can reproduce the error again?
what is reason of emergence of a mistake?