This time the FPE is caused by the case that the rho component (=x*x + y*y) is negligible compared to the z component, such that
m-z = 0.0 to double-precision (where m = sqrt(rho*rho + z*z)).
=x*x + y*y
m-z = 0.0
m = sqrt(rho*rho + z*z)