> Date: Sat, 29 Jul 2017 12:34:46 -0400
> From: Mark Oteiza <mvoteiza@udel.edu>
> Cc: emacs-devel@gnu.org
>
> >So I think the problem happens in unidata-word-list-compress, and it
> >happens because make-vector, which that function calls always returns
> >the same vector, so the vectors used by that function and created by
> >it are all messed up.
>
> I don't follow: why does it always return the same vector?

That's how I understand what the byte compiler does when you declare
that function "pure".