If an employee of a school district, including a district having the merit system as outlined in Article 6 (commencing with Section 45240) of Chapter 5, employed in a position requiring certification qualifications is assigned to a position in the classified service of the same district, the employee shall retain all sickness and injury, sabbatical leave, and other rights and benefits. All seniority and tenure rights accumulated by the employee at the time of assignment to the position in the classified service shall be secured to the employee during the period of time he or she occupies a position in the classified service. The employee’s return to certificated service at any time shall be treated as if there had not been an interruption in his or her certificated service.