related products sometimes messed up

-- HikaShop version -- : 2.4.0
-- Joomla version -- : 3.4.1
-- PHP version -- : 5.3.27
-- Browser(s) name and version -- : chrome
-- Error-message(debug-mod must be tuned on) -- : related products sometimes messed up

There is a stange problem that the related products in backend sometimes are messed up
for example,I choose 4 items for one product as "related products",but one or two days later the "related products"list become very long even to 26 products.(in this product page you can only see 4 related products ,that is because I restricted it and don't display the pagination under related products mudule)
Can you help fix it?
Thank you very much.
Jacky

Thank you Jerome,I uncheck this option and see if it works.