Why's it a mac problem? I'm confused.
Also are you on holiday yet? Hope you booked it early!
Yeah, been off all week.
Reason it's a Mac Problem: Depth precision, and more specifically near-clipping distance. Traditionally, there was a rule of thumb that your near clip distance needs to be as far out as possible, as it's the main thing that affects Z-precision. Because of the equation used, if your near clip is 10cm away, you use up 50% of your number range over the next 10cm, 25% over the next 20cm, and so on (this isn't exactly right but with a big draw distance it's close enough).
More recently, some clever person realised that if you use floating point depth, and use 1=near, 0=far instead of the traditional 0=near, 1=far, the increasing precision of floating point close to zero almost perfectly balances the other effect (the precision ends up kind of a wiggly line but it hovers around the ideal value). Depth precision issues solved, basically, with no downsides, and you can move the near clip distance to 1mm or whatever, set far clip to infinity, and no one cares. At that point you can put a helmet over the camera without worrying that a slightly wider monitor will cut holes in it.
Ok, so there's one downside: OpenGL traditionally uses -1=near, +1=far, which puts the extra precision in the middle even if you reverse it. To benefit from this new trick, an extension was added to make it clip at 0 and 1, but Macs are locked to a version of OpenGL that doesn't have that feature. IIRC it might also not have floating point depth buffers either. Pain in the backside really.