"postgresql-9.0-801.jdbc4.jar" Causing "Error committing transaction. Cause: org.postgresql.util.PSQLException: Cannot commit when autoCommit is enabled." Exception

Hello list,

. Postgresql8.3

. mybatis-3.0.5-SNAPSHOT.jar
. mybatis-spring-1.0.1-SNAPSHOT.jar
. spring3.0.5

. postgresql-9.0-801.jdbc4.jar

SqlSession sql_session = sqlSessionFactory.openSession(false);
....
sql_session.commit();

applicationContext-mybatis.xml

<bean id="dataSource"
class="org.springframework.jdbc.datasource.DriverManagerDataSource">
<property name="driverClassName" value="${driverClassName}" />
<property name="url" value="${url}" />
<property name="username" value="${username}" />
<property name="password" value="${password}" />
</bean>

When update/insert/delete is called, always got:
===================================================
### Error committing transaction. Cause:
org.postgresql.util.PSQLException: Cannot commit when autoCommit is enabled.

While for "8.4-702 JDBC 4", the same codes, no error at all.

Is there anything need to be configured if using
"postgresql-9.0-801.jdbc4.jar"?

Thanks a lot!
Emi