Seg Fault in backend after beginning to use xpath (PG 9.0, FreeBSD 8.1)

Our developers started to use some xpath features and upon deployment
we now have an issue where PostgreSQL is seg faulting periodically.
Any ideas on what to look at next would be much appreciated.

FreeBSD 8.1
PostgreSQL 9.0.3 (also tried upgrading to 9.0.4) built from ports
Libxml2 2.7.6 (also tried upgrading to 2.7.8) built from ports

pgsql logs show:
May 1 17:51:13 192.168.20.100 postgres[11862]: [94-1] LOG: server
process (PID 62112) was terminated by signal 11: Segmentation fault

syslog shows:
May 2 20:29:16 db3 kernel: pid 49956 (postgres), uid 70: exited on
signal 11 (core dumped)
May 2 21:06:37 db3 kernel: pid 39086 (postgres), uid 70: exited on
signal 10 (core dumped)

Checking out postgres.core and we see:

(gdb) bt
#0 0x00000008f5f19afd in pthread_mutex_lock () from /lib/libthr.so.3
#1 0x0000000800d22965 in xmlRMutexLock () from /usr/local/lib/libxml2.so.5
#2 0x0000000800d717e1 in xmlDictReference () from /usr/local/lib/libxml2.so.5
#3 0x0000000800d74ba5 in xmlSAX2StartDocument ()
from /usr/local/lib/libxml2.so.5
#4 0x0000000800ccee5f in xmlParseDocument () from /usr/local/lib/libxml2.so.5
#5 0x0000000800ccef85 in xmlDoRead () from /usr/local/lib/libxml2.so.5
#6 0x000000000076b58d in xpath ()
#7 0x00000000005880e4 in GetAttributeByNum ()
#8 0x0000000000588e91 in GetAttributeByName ()
#9 0x00000000005850a3 in ExecProject ()
#10 0x000000000058c5e4 in ExecScan ()
#11 0x0000000000584a2d in ExecProcNode ()
#12 0x000000000059bfc8 in ExecLimit ()
#13 0x00000000005848f5 in ExecProcNode ()
#14 0x0000000000583049 in standard_ExecutorRun ()
#15 0x000000000067630d in PostgresMain ()
#16 0x0000000000677921 in PortalRun ()
#17 0x0000000000672ea4 in pg_parse_and_rewrite ()
#18 0x0000000000675354 in PostgresMain ()
#19 0x0000000000626afb in ClosePostmasterPorts ()
#20 0x0000000000627a8e in PostmasterMain ()
#21 0x00000000005bbea7 in main ()
(gdb)

Ideas? Need more info?

Thanks,
Alan