I think it started about 2-3 days ago -- On SO I noticed when I click on a question, and then click "Back" (I use the mouse button, but that's not really relevant), I have to click it twice to get back to the question list.
If you click on question, notice how a "#" is appended to the end of the URL. If you click back once, it goes away. Then you have to click back again to get back to the questions.
Is it just me, or is this new? What is the point? It makes navigation a little frustrating.
It has been noted in Hash at the end of question URLs but I'm specifically bringing it up because of the impact on navigation. But if that answer is correct and it'll go away in a week or so, I suppose its a non-issue.