First, we should all agree that security interests are disclosable in the Fed box. If your state's law considers the right to setoff a security interest it should definitely be disclosed there.
Also look to the Commentary, 2(a)(25):
"1. Threshold test. The threshold test is whether a particular interest in property is recognized as a security interest under applicable law. The regulation does not determine whether a particular interest is a security interest under applicable law. If the creditor is unsure whether a particular interest is a security interest under applicable law (for example, if statutes and case law are either silent or inconclusive on the issue), the creditor may at its option consider such interests as security interests for Truth in Lending purposes."
There is certainly room to justify the disclosure, in my opinion anyway. But I'm no attorney. You might tactfully ask the examiner in charge to verify his/her findings with his/her supervisor since (I make assumptions here)this has not been a problem in the past, appears to be an accepted practice and allowed under the Commentary.
Opinions stated are not necessarily that of my employer.