Dear greigi,
I like your comments "auditor's responsibility to validate why yr input is unacceptable" & "Can you show me, specifically, where in the Standard that is stated?"
As I mentioned earlier, the options may relate to the specifics of any disagreement.
But, in general, how can it not be the case ? It rules to competency.
(Auditors seem to prefer the term “justification” rather than “validation”.)
For example, from the BRC food standard (v6) –
3.1 Calibrating auditors
A key component of the scheme is the calibration of the auditors to ensure a consistent understanding and
application of the requirements. All Certification Bodies are required to have processes to calibrate their own auditors
.
etc
From a FS viewpoint -
Validation (verb; to validate, ratify; valid, sound, defensible of reasonable
objection – Oxford English Dictionary)
Definition: Obtaining evidence that the elements of the HACCP plan are effective.
Explanation: Validation is concerned with obtaining evidence that the elements of the HACCP
plan will be effective; as such, validation should be targeted at the assessment of the scientific and
technical inputs into the HACCP plan. Validation should ensure that the information supporting
the HACCP plan is correct – that the production facility is “going to do the right things” – thus
enabling compliance with food safety policy. Evidence to support HACCP plans can come from a
wide variety of sources.
Validation provides evidence to support the HACCP plan and therefore takes place before
implementation and after alterations. As new scientific information comes to light, the
assumptions on which the validation is based should be reassessed. Where necessary such
reassessment must result in the amendment of the provisions laid down. When this is the case,
changes must be validated against this new information. Any change to the HACCP plan should
be fully incorporated into the documentation and record keeping system so that accurate up-to-
date information is available.
Where it is not possible to justify (validate, defensible of reasonable objection) an element of the
HACCP plan, there is only one option: modify the plan.
(ILSI 2001)
The key word is evidence.
And what is the Auditor’s modus operandum ? – “show me the evidence”.
What's good for the goose .........
Charles.C
PS - not saying that auditors expect/like to be challenged, quite the reverse. IMEX, their technical knowledge of your process is often likely to be skimpy. And they know it. 
PPS - haven't read the other post yet so no comments possible yet. 
P3S - Just realized I misinterpreted the top quote, thought the 2nd half of sentence was a follow-up question 
.
to the forum. Without specifics it is hard to give specific advice as to how to counter this as the "devil is in the details". But auditors having different opinions is a challenge for most of us in food safety and responsible for a fair amount of alcohol that is consumed. 
