setf not working

Hello,

yesterday, I fell on something extremely weird, or at least, which I currently fail to understand. Basically, after a (defvar *var*), there are times when (setq *var* '(0 0)) doesn't work (the previous value of *var* remains in effect).

I cannot currently provide a minimal example because the situation involves several levels of nested macro / function calls in code I didn't write (*var* is solely mine though).

At first, I thought I had fallen on a compiler bug, but I get the same behavior with at least 3 lisp implementations.

I ultimately found a workaround, consisting in using (list 0 0) instead of '(0 0) in the assignment. I'm hoping this would be a clue to someone here to get at least a direction for investigating...

Thanks.