The winbind idmap_rid backend is not being built. This is imho an important advanced feature documented on the Official HOWTO Collection (check bug's URL), and not available in gentoo's ebuilds. To explicitly enable it one must add '--with-shared-modules=idmap_rid' in ${myconf}
*** Bug 106845 has been marked as a duplicate of this bug. ***
Created attachment 68975 [details, diff] patch for samba-3.0.14a-r2.ebuild
Created attachment 68976 [details, diff] patch for samba-3.0.20-r1.ebuild
I've tested only 3.0.14a-r2
included in 3.0.20a, thanks