AutoLockBox - Negative Receipts

We have recently implemented the Automated Lockbox program with one our Financial Institutions.  One of the areas where we have experienced an issue has been around the ability to receive and process negative receipts.  It appears that the process that we have configured works well when the negative receipt is received and applied against a valid credit memos.  If the record appears to be an invalid credit memo, the record basically fails to import and then we have manually adjust the receipt amount to get the record to import.  I'm reaching out to see if you have encounted negative receipts