bug in root finding?

[Jon Danielsson <jond at rhi dot hi dot is>]

I am using gsl 1.0 on RH7.2, and encountered the problem that when
the rootfinder (gsl_root_fsolver_alloc (gsl_root_fsolver_brent);
finds the solution immeately, i.e. its brackeded between -100,100 
on third function evaluaiton it zero, which is the exact solution, but
then fails to recognize the fact, loops until max_iter is reached

here is the codefragment

	gsl_root_fsolver *s;
	gsl_function F;
	struct FRho_params params = {b,lambda,rbar,gamma};
	F.function = &FRho;
	F.params = &params;
	params.b=b;// = {d1,lambda,rbar,gamma};
	s = gsl_root_fsolver_alloc (gsl_root_fsolver_brent);
	gsl_root_fsolver_set (s,&F, -100,100);
	do {
		iterations++;
		status = gsl_root_fsolver_iterate (s);
		r = gsl_root_fsolver_root (s);
		x_lo = gsl_root_fsolver_x_lower (s);
		x_hi = gsl_root_fsolver_x_upper (s);
		status = gsl_root_test_interval (x_lo,x_hi, 0, 0.00001);
	}
	while (status == GSL_CONTINUE && iterations < max_iterations);

and the function

nnuble FRho (double x, void *params) {
	struct FRho_params *p = (struct FRho_params *) params;
	double  b= p->b;
	double lambda = p->lambda;
	double  rbar= p->rbar;
	double  gamma= p->gamma;
	double res=0.0;
	res= (x+lambda*(1-b)) - lambda * FN(sqrt(gamma)*(x-rbar));
	return res;
}
double FN(double x){
	return 0.5+ gsl_sf_erf (x/sqrt(2.0))/(2.0);

}