FWIW, Gentoo bug number is 199450.
Also Debian Tag 451839
and (the important one) Samba bug 5087
Discussion if this situation on the samba list dated 11-16 just appeared on Nabble (watch the wrap):
http://www.nabble.com/-samba-bugs@samba.org:-DO-NOT-REPLY--Bug-5087--Crash-o... after-upgrade-to-3.0.27--t4822039.html
Apparently their QA never tested a unix-unix situation. I suspect a fully tested fix will be coming shortly from samba.org since they seem very aware of the issues.
BTW, there are no known exploits <yet> with the old version, so if you are running mixed use samba it is probably safe to revert to the old rpms. YMMV.
regards,
benm