ClassCastException with LargeObjectAPI and Tomcat Connection Pool (DBCP)

Hello list,

I configured successfully a PostgreSQL 7.2.3 connection pool with JNDI
DataSource following the Tomcat docs (v 4.1.12).
But when I try to use the returned connection with the LargeObjectAPI,
tomcat gives me a ClassCastException (runtime), in the following line:

LargeObjectManager lobj =
((org.postgresql.PGConnection)db).getLargeObjectAPI();

I tried using pgjdbc2.jar, in which case instead of
org.postgresql.PGConnection, it only works with org.postgresql.Connection.
With pg73jdbc3.jar, and using org.postgresql.PGConnection, the same
Exception occurs.
I also tried with a compiled JDBC jar from the 7.3 sources, with no luck.

I don't understand why the connection works with non-LargeObject SQL and
fails here. I have the same jars working with the LargeObjectAPI without the
Tomcat DBCP.
Any help is appreciated. Has anyone successfully configured a tomcat DBCP
with PostgresSQL and used LOs with it?

Thank you,

João Filipe Plácido