Exchange Gain/Loss Account entries generated in stand-alone Credit Memo in Accounts Receivables

We have created on-account (stand-alone) credit memo with foreign currency. After accounted the transaction, found 2 lines in SLA for exchange gain/loss whereas the entered currency value shows as 0 and accounted currency value shows with the exact receivable event line's balance for both exchange gain/loss lines.

As per our understanding, exchange gain/loss will be generated if there is any difference in the exchange rates between the events (Invoice-Receipt/ Credit Memo-Adjustments). But without any such event, the Credit Memo accounting entries shows the exchange gain/loss lines.

We want to know the standard system behavior and justification.