Cal. Educ. Code § 24018

When a disabled member returns to work in his or her former position of employment or in a comparable level position and within six months of return experiences a recurrence of the original disability, that can be medically substantiated, it shall be considered, for the purpose of determining the duration of the disability, that the condition had its onset as of the date the member first became disabled. The former disability allowance under this part shall again become payable as of the later of the first day of the month in which the recurrence of the disability occurred or the last day of creditable service for which compensation is payable to the member provided the member complies with the provisions of Section 24003.