GSA Schedule - USPS Task Order - T&Cs?

Q: What terms and conditions apply to a task order placed by the USPS under a GSA Schedule contract? 

The USPS KO asserted that GSA Contract (FAR) clauses are the same as the USPS clauses and the only difference is the clause number. Therefore, the KO is unwilling to address order of precedence in the agreement.

Although the USPS clauses & provisions do largely track the FAR, they are definitely not the same. The USPS task order includes all the terms and conditions that would be required for a USPS purchase -- i.e. the entire procurement process and task order fulfill the USPS "Supplying Principles and Practices" requirements. And USPS is not subject to FAR in any event.

Have you encountered this before? How are we supposed to understand the GSA T&Cs read alongside the USPS task order T&Cs?

I've done my level best at finding this answer through legal research, but I've come up short. Hoping this group can offer some practical guidance from your experience -- or show me what I missed!

Thanks in advance.