In a March 22, 2017 Federal Court of Appeal case (Mosley vs. Attorney General of Canada, A-130-16), the Court found that a lump-sum retroactive CPP benefit payment was paid or payable on a periodic basis.
By allocating the CPP benefit payment to the period to which it related, the taxpayer had received an overpayment of Employment Insurance (EI) benefits (as CPP benefits should be deducted from the EI benefits an individual receives). As such, the individual would be required to repay the excessive EI benefit payments.
For further information see Video Tax News Monthly Tax Update Newsletter, Issue No. 429