There is a Microsoft Azure banner style advertisement (present on several sites, targeted to Dutch speaking users it appears) that breaks the behaviour of the back button. It adds the page URL to your history for a second time, so the back button first refreshes the page, and then makes you go back to the previous page on the second click.
I also reported this as an answer here, for the sidebar ad. I decided to make a new post, seeing there was no attention for the answer there, and the OP of that post appears to be on leave.
Ad in question on Code Review:
This ad is also seen on Super User:
This ad is also seen on gis.stackexchange.com: