Deadlock in vacuum (check fails)

I found following strange error on gothic moth:

================== pgsql.22658/src/test/regress/regression.diffs
===================
***
/zfs_data/home/postgres/buildfarm/gothic_moth/HEAD/pgsql.22658/src/test/regress/expected/vacuum.out
Tue Jan 12 22:06:13 2010
---
/zfs_data/home/postgres/buildfarm/gothic_moth/HEAD/pgsql.22658/src/test/regress/results/vacuum.out
Tue Jan 12 22:35:25 2010
***************
*** 94,99 ****
--- 94,103 ----
-- only non-system tables should be changed
VACUUM FULL pg_am;
VACUUM FULL pg_class;
+ ERROR: deadlock detected
+ DETAIL: Process 5913 waits for AccessExclusiveLock on relation 2662
of database 16384; blocked by process 5915.
+ Process 5915 waits for AccessShareLock on relation 1259 of database
16384; blocked by process 5913.
+ HINT: See server log for query details.
VACUUM FULL pg_database;
VACUUM FULL vaccluster;
VACUUM FULL vacid;

Detail here:

http://www.pgbuildfarm.org/cgi-bin/show_log.pl?nm=gothic_moth&dt=2010-01-12%2021:06:01

Zdenek