Subversion on a samba share

We have a couple of people who insist on using a shared checked out copy of
subversion. E.g. they have a samba share that they all use together (with
default permissions for new files 660 and all users in the same group).

svn update and other commands access the .svn directory and try to modify
permissions there. The problem with taht is that only the owner of a file is
allowed to change permission, it's not enough to be in the correct group.

Is there a way to tell subversion not to play with the permission of files?
The alternative, of forcing all samba users to the same user on the
filesystem, isn't exactly nice.

Enno.