If you are having a Mac issue, you might want to go over to blenderartist.org to find a solution there.
There are many Mac users/developers over there that may be able to help you.
You can even upload the file so people can test it out!
I'd say that's your best bet...getting it tested by other mac users.

If this is a new issue, you might want to report this bug...someone might get it fixed right away.

I know that this is a non issue with Windows or Linux...2.49 or 2.50.
Works fine for me.

Are you SURE your separating the the object?
Naming each separated object differently?
Exporting in "Object" mode? Not in "Edit" mode?

Hope you find a solution.