pg 8.3.7 libxml trying to free NULL pointer

This is CVS HEAD 8.3, Debian package 8.3.7 also affected.

libxml2: 2.7.3.dfsg-1 current version in debian testing.

postgres=# select version();
version
-----------------------------------------------------------------------------------
PostgreSQL 8.3.7 on i686-pc-linux-gnu, compiled by GCC gcc (Debian 4.3.3-3) 4.3.3

./configure --prefix=$HOME/inst/pg-dev --enable-nls --enable-debug --enable-depend --enable-cassert --enable-thread-safety --with-pgport=5433 --with-libxml --with-libxslt

postgres=# select xpath('count(//)', '<a></a>'::xml);
server closed the connection unexpectedly
This probably means the server terminated abnormally
before or while processing the request.
The connection to the server was lost. Attempting reset: Succeeded.

TRAP: FailedAssertion("!(pointer != ((void *)0))", File: "mcxt.c", Line: 580)
LOG: server process (PID 30335) was terminated by signal 6: Aborted

Program received signal SIGABRT, Aborted.
0xb7f90424 in __kernel_vsyscall ()
(gdb) bt
#0 0xb7f90424 in __kernel_vsyscall ()
#1 0xb7c59640 in *__GI_raise (sig=6) at ../nptl/sysdeps/unix/sysv/linux/raise.c:64
#2 0xb7c5b008 in *__GI_abort () at abort.c:88
#3 0x082efcae in ExceptionalCondition (conditionName=0x83d6832 "!(pointer != ((void *)0))",
errorType=0x83237a2 "FailedAssertion", fileName=0x83d682b "mcxt.c", lineNumber=580) at assert.c:57
#4 0x0830f1cc in pfree (pointer=0x0) at mcxt.c:580
#5 0xb7e6e5d2 in ?? () from /usr/lib/libxml2.so.2
#6 0x00000000 in ?? ()

--
Sergey Burladyan