Rendering Hair Particle in 2.64a

I’m using official build 64-bit version of Blender 2.64a under Ubuntu 12.10 and when I try to render a simple “hairball”, the highlight of the hair somehow seem to come out wrong.
However, if I render the same file under 32-bit environment (32-bit official build 2.64a with Ubuntu 12.10 32-bit), it comes out correct; or at least seem nicer then the 64-bit version.
I had attached 2 files each showing the result under different version.
Has anyone get a problem like this? Am I setting something wrong?
Thanks in advance.