La conexión MySQL no se cerrará

Has probado:

      using (MySqlConnection con = new MySqlConnection(ConfigurationManager.ConnectionStrings["mysqlCon"].ConnectionString))
      {
           con.open();
           MySqlDataAdapter DataDTTables = new MySqlDataAdapter(MySQLCommandFunc)
           DataDTTables.SelectCommand.CommandTimeout = 240000;
           MySQLCommandFunc.Connection = con;
           DataDTTables.Fill(DTTableTable);
           con.close();
     }

?