  Contrary to the opinion of J. Polchinski [Phys.Rev.Lett. {\bf 66}, 397-400
(1991)], the phenomenon of superluminal messages in nonlinear versions of
quantum mechanics is not a specific difficulty in a class of theories
formulated by S. Weinberg [Ann.Phys. (N.Y.), {\bf 194}, 336-386 (1989)]. It
appears in all schemes which try to enlarge the orthodox class of observables,
while conserving the traditional structure of the pure and mixed states.
