When selecting Search Order as "most recent topics first, the results are displayed in descending date order but only within board. So it looks like the actual sort being applied is Board then Post Date. I'm not sure if this is a bug or a 'feature'. For example search for "HomePhone" with the "most recent topics first" selected. Look down the results and you will see the post dates getting older, while the results are from the same Board. Then, when teh Board changes, the dates get newer again. In the above example search that should occur after about 7 items.