I don't know why you guys have to download the map again and again. Maybe some problem with the file-structure of macs.
Then, I do not know anything about macs, so I think we can not help you there. I hope the next version works better for you.
It's not myself that has to DL again and again, it is other people.
I'll explain:
New version comes out - two people go and download it. One has a mac (If that is in fact the issue) and the other has a PC. The guy with the mac, being the smart, intelligent, sensible (For buying a mac obviously) guy volunteers to host. He hosts the game, the PC man joins, and begins DL'ing. Both guys go "wtf..?!" cuz' they just DL'd the same version from the same site! Regardless, they wait, PC guy finishes, and they start.
They to re-host for whatever reason. Mac guy hosts again, PC guy does NOT have to DL. Before they start, another PC guy joins - DL'd from same website, same version, he has to DL. They wait for him, then start.
Once again, they re-host for whatever reason, and the 1st PC guy says.. "I'll just host to solve the issue!" So he does, and neither Mac guy or 2nd PC guy has to DL. Another Mac guy joins (Same conditions as 2nd PC guy) and does not have to DL.
Hope you enjoyed the story-version of the issue

! I just started and kept rolling with it!