I have donors who have signed up to pay for their memberships in quarterly installments. When their 4th (last) payment is processed, there is a failed transaction created in addition to a successful one. This means that my members are getting a failed payment notification even though their payment has succeeded.
Installment payments are tricky, so it's hard for us to say exactly where along the way Paypal is getting the idea to try to process two transactions at the end of the plan. We're not currently prioritizing this to be worked on.