Bug in pgjdbc2 ? org.postgresql.PG_Stream.flush(PG_Stream.java:355)

Hello,
I test a jsp script with ab -c 50 -n 10000 ( 50 simultan connection) an
sometimes I receive an exception:
    An I/O error has occured while flushing the output - Exception:
    java.net.SocketException: Socket closed Stack Trace:
    java.net.SocketException: Socket closed at
    java.net.SocketOutputStream.socketWrite(SocketOutputStream.java:99) at
    java.net.SocketOutputStream.write(SocketOutputStream.java:136) at
    java.io.BufferedOutputStream.flushBuffer(BufferedOutputStream.java:69) at
    java.io.BufferedOutputStream.flush(BufferedOutputStream.java:127) at
    org.postgresql.PG_Stream.flush(PG_Stream.java:355) at
    org.postgresql.core.QueryExecutor.sendQuery(QueryExecutor.java:135) at
    org.postgresql.core.QueryExecutor.execute(QueryExecutor.java:64) at
    org.postgresql.Connection.ExecSQL(Connection.java:398) at
    org.postgresql.jdbc2.Statement.execute(Statement.java:130) at
    org.postgresql.jdbc2.Statement.executeQuery(Statement.java:54) at
org.postgresql.jdbc2.PreparedStatement.executeQuery(PreparedStatement.java:99)
at _test__jsp._jspService(_test__jsp.java:102) at

    This is test.jsp:
 try
 {

          Class.forName("org.postgresql.Driver"); //load the driver
 }
  catch (ClassNotFoundException e)
    {
                 eroare="Eroare 1"+e;
                  out.println(eroare);
             return;
     }

     try
    {


        dbconn=DriverManager.getConnection("jdbc:postgresql://"+DB_HOST+"/"+DB_NAME,
        DB_USER,DB_PASS);

           dbmd = dbconn.getMetaData();
            sql= new java.sql.PreparedStatement[10];

    }
     catch (SQLException e)
     {
         eroare="Eroare 2"+e;
         out.println(eroare);
         return ;
     }
    java.sql.ResultSet rez;
     for (int j=0;j<10;j++)
    {


         try
        {
                sql[0] = dbconn.prepareStatement("select * from cat");
                rez=sql[0].executeQuery();
        }
        catch (Exception e)
        {
                eroare="Eroare 3"+e;
                 out.println(eroare);
             inchide();
            return;
        }

        try{
            while (rez.next())
            {
                out.println(", "+rez.getString("id"));
            }
        rez.close();
        sql[0].close();

        }
        catch(Exception e)
        {
             inchide();
          out.println("Eroare next"+e);
        }
    } //end for

    try
    {
        dbconn.close();
    }
     catch(Exception e)
    {
        out.println("Eroare inc"+e);
    }

    out.println("OK");


   Please, help me

  Sorin