newLISP v.10.7.1 64-bit on Linux IPv4/6 UTF-8 libffi, options: newlisp -h
> (= 'A 'A)
true
> (= 'A 'B)
nil <--------------- !!!
> (define (Test A B C))
(lambda (A B C))
> (++ (find 'D (first Test)))
1
> (= 'A 'A)
true
> (= 'A 'B)
1 <---------------- ???
Apparently ++ manages to increment nil so now the value of nil is 1.
It also appears to require a compound set of circumstances for allowing ++ increment nil, so: Well done, for finding this problem.