I had the same problem like Theant with Sj Responsive Content for K2 - infinite scrolling with a lot of duplicated articles. I found out, that the problem was related to cache settings in Joomla. When I changed cache settings from progressive to conservative in General Settings, it started to work fine - no duplicates anymore.
I had a look on your demo site and I see a sort of the same problem:
demo.smartaddons.com/#sj-k2-content-res
For example: "Giton sazi oken" article appears - twice, and "Okiten nusut xite" - three times.