Duplicates when sorting by date

duplicate when you run a select query data from a table sorted by date and ustnovki limit for pagination.

http://joxi.ru/GrqWO1SNJWgd2z

http://joxi.ru/Rmznp9FWJkobmO

SELECT iblock.ID AS ID, iblock.TIMESTAMP_X FROM b_iblock_element iblock WHERE iblock.ACTIVE = ‘Y’ AND iblock.ACTIVE_TO > ‘2016-03-29 10:54:00’ AND iblock.IBLOCK_ID = 39 ORDER BY iblock.TIMESTAMP_X DESC LIMIT 20, 10;
SELECT iblock.ID AS ID, iblock.TIMESTAMP_X FROM b_iblock_element iblock WHERE iblock.ACTIVE = ‘Y’ AND iblock.ACTIVE_TO > ‘2016-03-29 10:54:00’ AND iblock.IBLOCK_ID = 39 ORDER BY iblock.TIMESTAMP_X DESC LIMIT 30, 10;