Ok, I suspected it was the desired behaviour!
First: when you use by folder i coded the PI to load all shown music on list, means, you are correct, if you see youre entire collection and hit "Select" all youre music will be loaded to playlist, if you want to load "Air" folder, try "Browse" button first, then "Select".
Ok, note that the same happens when you first select "music" then one of predefined methods "By Artist, By Title, By Album...", then "browse" button; you select a song and you're back to playlist screen with music playing. If you click again on audio you fall in the previous case! So you have the list of predefined methods but regardless of what you choose you'll get the playlist page with an empty playlist.. I hope I made myself clear!
Second:to browse using the predefined methods, "By Artist, By Title, By Album etc." use "Browse" button, instead of double click on list. i'll see if theres a bug on the skin or the PI, to see why double click is not working correctly.