SharePoint ACL on OSX Lion Server - Posix group always takes over ACLs
Solution 1:
I'm going to post this as an answer because this workaround fixes all access issues for us.
We've basically stopped trying OD Groups for permissions altogether.
It works perfectly if we add OD Users to the share and propagate down (after resetting all ACL to clean up the previous mess).
When we give permissions based on Users everything works fine as expected and the ACL takes over the posix permissions.
Really not sure why the group doesn't work. We thought it might be because the OD group doesn't match a local group on the respective client machine but creating an explicit local group doesn't seem to fix it (though we only tried matching the group name, not the gid).
Anyway, hope this helps someone.
A side note: It use to work perfectly fine on Snow Leopard server, this is just on Lion server.