Alethra is correct. Only 1 file is saved at a time. So after someone updates their map data. Then everyone in the party has to copy it before anyone else touches the update. If someone hits the update map area before everyone copies that data,... things get messed up.

If you have a large party it takes awhile to get everyones data.

I think, if I remember right, it goes by who last saved to the table. I could be wrong, though. So I guess you would need to copy what's there, then add your own ... which includes what you copied. Then the next person, then next. Then it should be complete and you can all go back and copy what is there without adding anything first. I don't know if that makes sense. I don't explain things well, sometimes.