file_mode and dir_mode options of CIFS filesystem driver don't completely work as expected for newly-created files or directories on shares that have "unix_extensions=no". https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=221081 Fedora kernel 2.6.20 with samba patch "reset mode when client notices that ATTR_READONLY is no longer set" from 2.6.21-rc applied.
Closing as FIXED.