Permanent employees who are promoted to a higher classification shall undergo the probationary period prescribed for the higher classification, but shall have the right to demote to their former classification in their former department if a vacancy in their former classification exists. If no vacancy exists, such employees shall be placed in the longest standing vacancy, as determined by the requisition form date, County‑wide. Should the longest standing vacancy entail “unusual” work hours, the employee shall have the one-time option of returning to the second longest standing vacancy should one exist. (“Unusual” shall mean work hours or work week dissimilar to those of the position from which or to which the employee was promoted.) If no vacancy exists, such employees shall displace the least senior employee as determined by Section 14. If no less senior position exists, then the employee shall be removed from County service.