Portrait N900 desktop, has anyone tried got this today and what does that mean??

About 2 hours ago I made a call and put it on the speakers, when I pushed end and clicked the the x to exit the contact screen, all the sudden my desktop was in the portrait mode and was able to scroll sideways with it to the next desktop screens. I was able to duplicate it about 7 times now, sorry I don't knew how to put screen shots.

Could someone duplicate and comment, please??