Code:
string stmp = "\n<rs:data ItemCount=\"6\" xmlns:rs=\"urn:schemas-microsoft-com:rowset\">\n   <z:row _x041a__x043b__x0438__x0435__x043d__x0442___x043a__x043e__x0434_=\"16440042770нс\" _x0424__x0438__x043b__x0438__x0430__x043b___x041a__x043e__x0434_=\"20706\" _x041a__x043e__x0434_=\"3049\" _x041d__x0430__x0437__x0432__x0430__x043d__x0438__x0435_=\"Татнефть У*С\" BdcIdentity=\"__bg01003300030043009300\" xmlns:z=\"#RowsetSchema\" />\n   <z:row _x041a__x043b__x0438__x0435__x043d__x0442___x043a__x043e__x0434_=\"16440042770нс\" _x0424__x0438__x043b__x0438__x0430__x043b___x041a__x043e__x0434_=\"20706\" _x041a__x043e__x0434_=\"5328\" _x041d__x0430__x0437__x0432__x0430__x043d__x0438__x0435_=\"*озница\" BdcIdentity=\"__bg01005300330023008300\" xmlns:z=\"#RowsetSchema\" />\n   <z:row _x041a__x043b__x0438__x0435__x043d__x0442___x043a__x043e__x0434_=\"16440042770нс\" _x0424__x0438__x043b__x0438__x0430__x043b___x041a__x043e__x0434_=\"20706\" _x041a__x043e__x0434_=\"5353\" _x041d__x0430__x0437__x0432__x0430__x043d__x0438__x0435_=\"Медуница\" BdcIdentity=\"__bg01005300330053003300\" xmlns:z=\"#RowsetSchema\" />\n   <z:row _x041a__x043b__x0438__x0435__x043d__x0442___x043a__x043e__x0434_=\"16440042770нс\" _x0424__x0438__x043b__x0438__x0430__x043b___x041a__x043e__x0434_=\"20706\" _x041a__x043e__x0434_=\"5357\" _x041d__x0430__x0437__x0432__x0430__x043d__x0438__x0435_=\"Оптовик\" BdcIdentity=\"__bg01005300330053007300\" xmlns:z=\"#RowsetSchema\" />\n   <z:row _x041a__x043b__x0438__x0435__x043d__x0442___x043a__x043e__x0434_=\"16440042770нс\" _x0424__x0438__x043b__x0438__x0430__x043b___x041a__x043e__x0434_=\"20706\" _x041a__x043e__x0434_=\"8372\" _x041d__x0430__x0437__x0432__x0430__x043d__x0438__x0435_=\"Артемьев ИП\" BdcIdentity=\"__bg01008300330073002300\" xmlns:z=\"#RowsetSchema\" />\n   <z:row _x041a__x043b__x0438__x0435__x043d__x0442___x043a__x043e__x0434_=\"16440042770нс\" _x0424__x0438__x043b__x0438__x0430__x043b___x041a__x043e__x0434_=\"20706\" _x041a__x043e__x0434_=\"8620\" _x041d__x0430__x0437__x0432__x0430__x043d__x0438__x0435_=\"Шифа\" BdcIdentity=\"__bg01008300630023000300\" xmlns:z=\"#RowsetSchema\" />\n</rs:data>\n";
            XmlDocument xd = new XmlDocument();
            xd.LoadXml(stmp);

            DataSet dsQuery = new DataSet();
            var node = xd.DocumentElement as XmlNode;
            XmlReader reader1 = new XmlNodeReader(node);
            dsQuery.ReadXml(reader1);

            var v1 = dsQuery.Tables["row"].Rows[4]["_x041a__x043e__x0434_"];
            var v2 = dsQuery.Tables["row"].Rows[4][dsQuery.Tables["row"].Columns[2].ColumnName];

The line with v1 throws an exception:

Column '_x041a__x043e__x0434_' does not belong to table row.


The line with v2 throws no exception, however it returns an empty value instead of expected integer value. I wonder why it happens and how to force dataset to work with my XML correctly?