No subject

Dec 27 19:54:18 SWDEV035 pgpool: 2012-12-27 19:54:18 ERROR: pid 18412: pgpool detected difference of the number of inserted, updated or deleted tuples. Possible last query was: "DELETE FROM JBM_MSG WHERE MESSAGE_ID = $1 AND NOT EXISTS (SELECT JBM_MSG_REF.MESSAGE_ID FROM JBM_MSG_REF WHERE JBM_MSG_REF.MESSAGE_ID = $2)"
Dec 27 19:54:18 SWDEV035 pgpool: 2012-12-27 19:54:18 LOG:   pid 18412: CommandComplete: Number of affected tuples are: 0 1

As you said, it seems your node 0 DB did not have a raw satisfied the
WHERE clause, while your node 1 had one row which satisfied it at that
time. I suggest to check tables used by JBoss right after failover to
see there's difference in table's data.
--
Tatsuo Ishii
SRA OSS, Inc. Japan
English: http://www.sraoss.co.jp/index_en.php
Japanese: http://www.sraoss.co.jp