Because it shows you the total upvotes when you upvote. Look over at the side bar and that 87 was the total number of upvotes, without the downvotes being subtracted. Refresh the page and it will show you the adjusted score.  I just upvoted, and the displayed scored jumped from 59 to 101.   SCP: 60 101 upvotes, 41 downvotes (71% upvoted it)  Once I refreshed the page, it reads 60.