bessely() sometimes returns bogus

I have found that bessely() with very large argument returns various results. For example,

julia> using SpecialFunctions

julia> bessely(1000.5, 7.745186719805684e8)
-1.65447992609e-312

julia> x = bessely(1000.5, 7.745186719805684e8)
1.3586779285536575e24

The assignment to `x` enhances the effect, though different answers are returned without assignment as well.

I am using `julia-v0.6.1` on x86_64 archlinux. The effect is less severe, but also present, on my macosx machine, which is running 0.6.1-pre3. Finally, on archlinux, I've also seen it with `v0.6.2-pre.2`, commit 247087d94c.