Thats relevant how?

I watched my Mac OS X 10.7.4 box count backwards this leap second. The time went to 00:00:00, then back to 23:59:59. At least Linux makes the effort to have the seconds never go backwards.

Mac OS X is a BSD variant, so there's every chance.

How does that follow? OS X runs an odd hybrid kernel (XNU) which is Mach and parts of BSD, but... this is a Linux kernel bug. There's an effectively zero chance of this impacting anything but Linux.

The kernel is not the only OS component relying on time that may have not considered this.

This is evidently a kernel bug. The fact that both operating systems rely on time isn't particularly relevant. Could there be time bugs in OS X? Certainly. But it wouldn't be this one. Windows relies on time too, so I don't see why you bring up the fact that OS X is a BSD variant.

BSD doesn't have an adjtimex syscall, so it's very unlikely for there to be a spinlock bug in the adjtimex syscall that doesn't exist.