A potential problem with small net expenses is that HSA custodians sometimes charge a fee to issue a distribution to the HSA owner, particularly if paid to the owner by check instead of by ACH transfer. If so, it might make sense to accumulate these expenses, even over several years, then obtain a single distribution to reimburse yourself for these accumulated expenses. A side benefit can be that the HSA holds the funds longer to grow tax free.
In the case here, it's even possible that the HSA custodian could treat the debit-card refund as a rollover. The problems with that are that a rollover must be completed within 60 days of the distribution and you are limited to one rollover in a 12-month period. HSA custodians seem really reluctant to issue corrected Forms 1099-SA even though they are required to do so when they accept a return of mistaken distribution. Perhaps some treat it as a rollover even when you have asked them to accept a return of mistaken distribution. So as TurboTaxBillMc suggests, it's best to avoid the possibility of a mistaken distribution in the first place. In fact, if you knew that the time of the distribution from the HSA the medical provider would be issuing a refund of some or all of the payment, it might not qualify as a mistaken distribution eligible for return to the HSA.
