After extensive debugging I found the bugs:Okay. Well like I said, I'm 90% sure that's just how PW3's rainfall system works. Ceph made a big deal about mountains creating "rain shadows" when he wrote it, among other effects, and this was heavily discussed in the Civ5 PW3 thread.
I did specifically allow PM to use the PW2 climate system (temperature and rainfall) with the PW3 terrain system (better-looking landmasses) because I recognized the major difference with the new climate system, and I knew that if I might want the old system, then others might too, heh.
But I don't think it's anything I did wrong in the port.
1.) Integer division instead of floating point division in the latitude from y calculation
2.) Only 6 monsoon neighbor plots (which is Civ5 hex setup) instead of 8 neighbor plots (as it should be in Civ4)
3.) Geostrophic rain deactivated (was commented out but disfunctional with the other bugs anyway)
4.) Bugs in the plot list generation for geostrophic rain (sorted geo map)
I have attached the file I debugged it on but since it is an adaption for C2C it has several other changes as well.