#1 In full screen mode you can still scroll up and down with the d-pad. Just so that you know...if you accidentally press left, then scroll up and down stops working until you press right again. I think this is because when you press left it goes to the feed side, but since it's not displayed in full screen mode you don't realize that.

#2 doesn't work because it still thinks that left and right changes between feed side and detail side. Try it, if you select the first feed, then put it into full screen mode, press left, then press down, change it back to split screen mode, you will see that the second feed is selected. Try it.

#3...have no idea.