Portal suddenly disappears?

While looking at pgpool-II user's complain, I see weired thing in the
PostgreSQL log.

Jan 14 10:04:57 dayrhegrdp005 postgres[25223]: [4559-1] LOG:  00000: statement: PREPARE pgpool19528 AS SELECT count(*) from (SELECT has_function_privilege('measure',
Jan 14 10:04:57 dayrhegrdp005 postgres[25223]: [4559-2]  'pgpool_regclass(cstring)', 'execute') WHERE EXISTS(SELECT * FROM pg_catalog.pg_proc AS p WHERE p.proname = 'pgpool_regclass'))
Jan 14 10:04:57 dayrhegrdp005 postgres[25223]: [4559-3]  AS s
Jan 14 10:04:57 dayrhegrdp005 postgres[25223]: [4559-4] LOCATION:  exec_parse_message, postgres.c:1159
Jan 14 10:04:57 dayrhegrdp005 postgres[25223]: [4560-1] LOG:  00000: statement:  pgpool19528
Jan 14 10:04:57 dayrhegrdp005 postgres[25223]: [4560-2] LOCATION:  exec_bind_message, postgres.c:1460
Jan 14 10:04:57 dayrhegrdp005 postgres[25223]: [4561-1] ERROR:  34000: portal "pgpool19528" does not exist
Jan 14 10:04:57 dayrhegrdp005 postgres[25223]: [4561-2] LOCATION:  exec_execute_message, postgres.c:1669

The portal "portal19528" was created by a bind message (pgpool-II uses
the identical name as the named statement) then subsequent
exec_bind_message failed to find the portal. Could it ever happen?
According to the user, PostgreSQL version is 8.1.23. Could it be a
source of problem?

Best regards,
--
Tatsuo Ishii
SRA OSS, Inc. Japan
English: http://www.sraoss.co.jp/index_en.php
Japanese: http://www.sraoss.co.jp