Sales Order Tax Date vs RMA Tax Date and line calculation

We started seeing that on RMA's which were created by copying from their original order (changing the order type to RMA) were having different tax calculations at the line level (more). Our process had not changed so we created an SR with Oracle and started looking into it.

Example:

Sales Order X1 is booked, shipped and invoiced 08-DEC-2017 with tax (totaling $5.00).

One year later 02-DEC-18 the sales order is returned so we copied X1 and changed the order type to RMA X2.  The tax rate for Denver increased so now the tax is $10.00. So we would be crediting the customer for more tax than they paid on their original order because the tax calculated is as of 02-DEC-18 with the rate increase vs as of 08-DEC-2017 when the tax rate resulted in $5.00