Intuit IPP QBO API Overwriting Customer's Default Tax Code when sending TaxCodeRef on Invoice

Question

• In the Quickbooks Online (QBO) web application, you can specify the Default Tax Code for that customer
• When you create an invoice, and mark the line items as taxable ("TAX"), and do NOT specify a transaction tax code ref, QBO will nicely apply the Default Tax Code to that invoice and calculate the correct tax accordingly.
• However, if you specify a transaction Tax Code Ref in an invoice, though the imported invoice in QBO uses that tax code and correctly calculates the taxes, it is also permanently updating the Customer's Default Tax Code in the customer profile.

Anyone know if this is a bug? Or if the way I am passing the tax code ref on the invoice is the issue?

Here is my Invoice creation XML that I post to the API:

<?xml version="1.0"?>
<Invoice xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://schema.intuit.com/finance/v3">
  <CustomField>
    <DefinitionId>1</DefinitionId>
    <Type>StringType</Type>
    <StringValue>15129</StringValue>
  </CustomField>
  <CustomField>
    <DefinitionId>2</DefinitionId>
    <Type>StringType</Type>
    <StringValue>13553</StringValue>
  </CustomField>
  <DocNumber>9316-O</DocNumber>
  <TxnDate>2016-05-12-06:00</TxnDate>
  <PrivateNote>15129 / Acme </PrivateNote>
  <Line>
    <LineNum>1</LineNum>
    <Description>Project: Acme </Description>
    <DetailType>DescriptionOnly</DetailType>
  </Line>
  <Line>
    <LineNum>2</LineNum>
    <Description>Part: 74827 - 8 ea. Down Rod and link 810 x 23 of:
1" x .25 wall alum. tubing;
Zinc plated R hand Threaded Clevis ;
Zinc plated L hand Threaded Clevis ;;

Part: 74830 - 8 ea. Down Rod and link 944 x 27.4375 of:
1" x .25 wall alum. tubing;
Zinc plated R hand Threaded Clevis ;
Zinc plated L hand Threaded Clevis ;;

Part: 74829 - 4 ea. Down Rod and link 943 x 24.8125 of:
1" x .25 wall alum. tubing;
Zinc plated R hand Threaded Clevis ;
Zinc plated L hand Threaded Clevis ;;

Part: 74831 - 20 ea. Link x 7.7 of:
Aluminum Mill 5052 .250Ga.;;

</Description>
    <Amount>1387.63000000</Amount>
    <DetailType>SalesItemLineDetail</DetailType>
    <SalesItemLineDetail>
      <ItemRef>19</ItemRef>
      <Qty>1</Qty>
      <TaxCodeRef>TAX</TaxCodeRef>
    </SalesItemLineDetail>
  </Line>
  <TxnTaxDetail>
    <TxnTaxCodeRef>5</TxnTaxCodeRef>
  </TxnTaxDetail>
  <CustomerRef>423</CustomerRef>
  <PrintStatus>NeedToPrint</PrintStatus>
  <EmailStatus>NeedToSend</EmailStatus>
  <BillEmail>
    <Address>test@test.com</Address>
  </BillEmail>
</Invoice>

UPDATE 1:

• We have 2 tax codes setup in QBO
• If the customer's default tax code is set to the first tax code option in the drop down list (DDL). And you create a new invoice, or send an update to an existing invoice that specify the Transaction Tax Code Ref that corresponds to 2nd tax code in the DDL in the UI, then the customer's default tax code is incorrectly updated to that second tax code, like stated above.
• However, if in the UI you set the Customer's Default Tax Code to the second tax code in the DDL, then send a new or updated invoice with a Transaction Tax Code Ref of the first tax code in the DDL, the customer's Default Tax Code is NOT updated...it stays as the 2nd tax code.
• List item

Answer 1

Please reference the following thread and answer:

https://intuitdeveloper.lc.intuit.com/questions/1372819-customer-default-tax-code-being-overwritten-by-invoice-transaction-tax-code-ref