Multiple posts are getting liked, after clicking on some selected posts

Question

I have used facebook like for voting on my contest website(http://halla.in), it was running fine until recently after one of user reported this. On this page (http://halla.in/entries.php?contest_id=MzE=) six entries are getting same likes, means if someone clicks on one of these 6 posts, then other five post's likes are also getting incremented. Each posts have unique url. I have never seen such strange thing, anyone experienced something similar before ? any hint or clue or suggestion would be of great help. thanks in advance.

Answer 1

That was a mistake on my part, I was using canonical urls, which was treating every url same.