unexpected close

we have a inhouse Java OLTP type application thats getting unexpected
errors.

PostgreSQL 9.2.5 is logging...
2013-11-09 13:03:10.945 role(at)db[13101]: ERROR: invalid message format
2013-11-09 13:03:10.945 role(at)db[13101]: STATEMENT: select * from t1
where t1_id = $1
2013-11-09 13:03:10.945 role(at)db[13101]: FATAL: invalid frontend message
type 0

2013-11-09 13:16:19.257 role(at)db[19291]: LOG: unexpected EOF on client
connection with an open transaction
2013-11-09 13:16:34.152 role(at)db[19352]: LOG: unexpected EOF on client
connection with an open transaction
2013-11-09 13:16:38.203 role(at)db[13161]: LOG: unexpected EOF on client
connection with an open transaction

2013-11-09 13:17:38.995 role(at)db[19523]: ERROR: invalid message format
2013-11-09 13:17:38.995 role(at)db[19523]: STATEMENT: select * from t1
where t1_id = $1
2013-11-09 13:17:38.995 role(at)db[19523]: FATAL: invalid frontend message
type 0

2013-11-09 13:17:40.622 role(at)db[19475]: ERROR: insufficient data left
in message
2013-11-09 13:17:40.622 role(at)db[19475]: STATEMENT: select * from t1
where t1_id = $1
2013-11-09 13:17:40.622 role(at)db[19475]: FATAL: invalid frontend message
type 0

this has been happening every few minutes, on a server thats getting
sustained 100s of small transactions/second but is only maybe 10% busy
peak. the clients are JDBC programs, and are getting this:

java.sql.SQLException: org.postgresql.util.PSQLException: An I/O
error occured while sending to the backend.
....stack dump....
Caused by: org.postgresql.util.PSQLException: An I/O error occured
while sending to the backend.
....more stack dump....
Caused by: java.net.SocketException: Socket closed
....more stack dump....

the server is 9.2.5...
PostgreSQL 9.2.5 on x86_64-unknown-linux-gnu, compiled by gcc (GCC)
4.4.7 20120313 (Red Hat 4.4.7-3), 64-bit

but it looks like the app was packaged with a rather old JDBC,
postgresql-8.3-604.jdbc3.jar
our java apps do only the most basic sql APIs, all data is numbers and
varchar, this jdbc worked fine with older versions.

is this a error likely because of this old JDBC with the newer 9.2 server?