A. If more than the correct amount of employer or member contributions is paid into the plan by an employer through a mistake of fact, the board shall return those contributions to the employer if the employer requests return of the contributions within one year after the date of the overpayment. The board may not pay an employer earnings attributable to excess contributions but shall reduce the amount returned to an employer pursuant to this subsection by the amount of losses attributable to the excess contributions.

B. On termination or partial termination of the plan, the accrued benefit of each member is, as of the date of termination or partial termination, fully vested and nonforfeitable to the extent then funded.