Positive Taxes getting calculated for Unreferenced Return Order based credit Memo

The Taxes amount and rules are correct but Positive Taxes getting calculated for Unreferenced Return Order based credit Memo.
On the Sales Return Order the Taxes are negative only.

The Negative Taxes are properly getting calculated for Standalone Credit Memo, AR invoice Based Credit Memo & referenced Return order credit Memo.

Rephrasing the issue for better clarity. 

In our system, taxes are calculated based on the assessable value.

In the case of an Unreferenced Return Order, the assessable value appears as positive, and taxes are being calculated as negative at the order level.  

However, when the Unreferenced Return Order is processed via AutoInvoice