It seems to be set back to front
Assuming you are reading this on Recent Posts, click "Profile" in the line under your Avatar
Then hover over "Modify profile" and a drop down menu appears - pick "look and layout"
Change whatever setting you have under "Show most recent posts at the top"+ click "change profile" - bottom RH corner
When "most recent posts at the top" is selected, I get the old posts first, and when it is de-selected I get the new posts on the top
I'm on Windows 7 and Internet Explorer other browsers may give different results