1-If you use "Select" (the button without the + sign) the song currently selected will be loaded (together with folder items) and automatically played. What you described happens when you use "select+" (only adds the current folder into the playlist, without changing the song currently playing). When you double click on a item RR executes "select" instead of "select+" -- the default skin should have BOTH buttons.
2-I just don't like that feature... frankly, why would anybody need to see the item that is being played highlighted in the playlist if it is on (big) display on top of the screen? I also found that such feature in MediaCar was quite buggy as I saw many times more than one item highlighted as the current song.