Wolfgang Walther <walther@technowledgy.de> writes:
> This is because the "must be superuser to alter replication users" 
> condition only triggers when the altered role already has isrepliaction, 
> so isreplication could very well be >= 0 here.
How do you figure that?  This is in an "else" path after
    else if (authform->rolreplication || isreplication >= 0)
so AFAICS it's impossible to get there.  If it isn't impossible,
we have a much bigger hole with respect to issuper.
            regards, tom lane