John,
That's an interesting approach. But, since you are talking IRS, shouldn't you be looking at disqualified persons instead of party-in-interest? I don't see former employee listed as a category of disqualified persons.
Rev. Proc. 2008-50 has a correction method for overpayments. It sounds like that may be how the TPA is correcting the overpayment failure.
QUOTE
Section 6.06(3) Correction of Overpayment failures. An Overpayment from a defined benefit plan is corrected in accordance with the rules in section 2.04(1) of Appendix B. An Overpayment from a defined contribution plan is corrected in accordance with the Return of Overpayment method set forth in this paragraph. Under this method, the employer takes reasonable steps to have the Overpayment, plus appropriate interest from the date of the distribution to the date of the repayment, returned by the participant or beneficiary to the plan. To the extent the amount returned to a defined contribution plan is less than the Overpayment adjusted for earnings at the plan's earnings rate, then the employer or another person must contribute the difference to the plan. The Overpayment, adjusted for earnings at the plan's earnings rate to the date of the repayment, is to be placed in an unallocated account, as described in section 6.06(2), to be used to reduce employer contributions (other than elective deferrals) in the current year and succeeding year(s) (or if the amount would have been allocated to other eligible employees who were in the plan for the year of the failure if the failure had not occurred, then that amount is reallocated to the other eligible employees in accordance with the plan's allocation formula). In addition, the employer must notify the employee that the Overpayment was not eligible for favorable tax treatment accorded to distributions from Qualified Plans (and, specifically, was not eligible for tax-free rollover).