Caarie - I have been talking with someone in-game who had similar problems (not on mac) but managed to fix it by replacing the affected maps with maps from 4.0 - I would like to try it (if you think it has any chance of working?) but unfortunately I didn't make a backup of 4.0 (or the initial 4.01 update on 29.06.2008) and the links available are only for the latest version (the one from the mirror in Sweden isn't working)...
from reading the posts here and on the bugtracker, there may also be discrepancies on which maps do and don't work between the various versions of OS X running on PPC. i.e. 10.3, 10.4 and 10.5 sound like they are having the same sort of problems but with different maps since the 4.01 update on 21.07.2008.