[boost] about bessel function

Hi all, I am testing the bessel function boost::math::cyl_bessel_j in gnu compiler with boost 1.51.0, I am testing boost::math::cyl_bessel_j(2000, 0.9) boost::math::cyl_bessel_j(4000, 0.9) the first one give zero but the second one gives infinity while it should give zero also. I wonder why it doesn't work when the order is bigger than 4000?