A person who retires under section 26 due to a duty incurred disability and who has been or is reinstated in active service shall again become a member of the retirement system from the date of the reinstatement. Upon reinstatement of the disability retirant to active service, any balance the retirant may have in the reserve for retired benefit payments at the time of reinstatement to active service shall be transferred from that reserve to the reserve for employee contributions and credited to his or her individual account in that reserve. Any service, on the basis of which his or her retirement allowance was computed at the time of retirement, shall be restored to full force and effect, and he or she shall be given service credit for the period of time he or she was out of service due to the disability.