The FS2_Open OS X port is based on the original icculus.org port code that tigital and I worked on. A rather large amount of the original code was changed or rewritten by me for FSO, the two main parts which remain all tigital's being the float byte-swap and the BSP swapping. Most of the changes that I've made also filtered back down to the icculus.org port, but in an effort to play nice I have never released an updated build for the icculus.org version myself, and tigital hasn't released one in quite a while. So, most of the bugs/problems with the icculus.org OS X port have actually been fixed, but there has never been a new build released with those fixes.
I'm still working of the FS1 icculus.org port, and when I get done with my current changes/fixes I plan to release a full set of FS1 & FS2 builds for Linux and OS X. No ETA on that though, I've been spending most of my time working on FSO instead.