Logging function calls to figure out lo_close log entries?

Given the following log entries:

May  7 09:40:05 vault pgqv[13698]: [353] DEBUG:  ProcessUtility: begin;
May  7 09:40:05 vault pgqv[13698]: [354] DEBUG:  query: SELECT COMPRESSED,
DATA FROM ATTACHMENTS WHERE ID=460739 AND ATYPE='X'
May  7 09:40:05 vault pgqv[13698]: [355] DEBUG:  query: end
May  7 09:40:05 vault pgqv[13698]: [356] DEBUG:  ProcessUtility: end
May  7 09:40:08 vault pgqv[13698]: [357] DEBUG:  query: begin;
May  7 09:40:08 vault pgqv[13698]: [358] DEBUG:  ProcessUtility: begin;
May  7 09:40:08 vault pgqv[13698]: [359] DEBUG:  query: SELECT COMPRESSED,
DATA FROM ATTACHMENTS WHERE ID=460739 AND ATYPE='X'
May  7 09:40:08 vault pgqv[13698]: [360] DEBUG:  query: end
May  7 09:40:08 vault pgqv[13698]: [361] DEBUG:  ProcessUtility: end
May  7 09:40:08 vault pgqv[13698]: [362] ERROR:  lo_close: invalid large obj
descriptor (0)
May  7 09:40:08 vault pgqv[13698]: [363] ERROR:  lo_close: invalid large obj
descriptor (0)
May  7 09:40:08 vault pgqv[13698]: [364] ERROR:  lo_close: invalid large obj
descriptor (0)
May  7 09:40:08 vault pgqv[13698]: [365] ERROR:  lo_close: invalid large obj
descriptor (0)
May  7 09:40:08 vault pgqv[13698]: [366] ERROR:  lo_close: invalid large obj
descriptor (0)

I'm trying to help some programmers figure out what portion of their java
code might be causing this, but I don't know java to help them debug their
code-- I was wondering if there is anything on the server end that I could
change to help them track this down.  They're using the jdbc that was
current shortly after the 7.2 release and the 7.2 server (they're still in
acceptance testing for 7.2.1).

They do turn autocommit off, and they've discovered that they may not have
been turning it back on explicitly so are going to make a change to that
portion of code.  Are there any other easy mistakes that people have made
that may result in the above behavior?

-ron