System has not created the Credit Memo from dispute

Summary:

We have come across a scenario where the AR invoice is for 51,150 AUD. Now, the user is submitting the dispute for 1.60 for specific line. So while submitting the dispute either we can enter dispute amount or dispute quantity. In our case the user is entering dispute amount as 1.60 AUD. While doing so the dispute quantity remains as 0 (zero) only.

Now, we created the dispute the dispute for 1.60 AUD but this time its against the full invoice and not for specific line on same invoice. For this scenario the system has created the credit memo from dispute.

Does anyone have experienced such thing, then please help us here to understand the system behaviour?