shouldn't crash on mac or other linux distros anymore
It was probably reproducible under Windows too. I'm sure that the OS wasn't the culprit, only quite "tolerant" drivers accepted your shader as it was. I'll give it another try when I'm at home.
Edit.: I've just tested it a few minutes under Windows 7 64 bits, Nvidia Quadro 600. It works correctly. You said that there is no shooting yet. I advise you to read this discussion
about collisions in FPS. To sum up, if you need a quick and dirty method to implement the shooting, just use rays, otherwise use multisampling (a posteriori discrete collision detection, easy to implement but expensive) or a priori continuous collision detection (harder to implement but more accurate, more efficient most of the time, supported by some physics engine). I quoted some articles in the thread above, I hope it will be helpful for you. Anyway, you can use the LibGDX 3D physics Bullet wrapper, maybe it is already the case.