The "lazy" auto-commit optimization (to avoid repeated setAutoCommit invocations on the driver/network/db)
does not work for datasource connections not enlisted in JTA transaction with no work done.

Example from the forums:
DataSource ds = getDataSource();
Connection con = ds.getConnection();
con.setAutoCommit(false); // not propagated to driver
con.rollback(); // driver throws an exception because autocommit is true.

The fix is trivial and probably originally a typo since rollback(Savepoint) has the correct code.

org.jboss.resource.adapter.jdbc.WrappedConection::rollback()
{

• checkStatus();
  + checkTransaction();
  mc.jdbcRollback();
  }