[DiapDealer]

When you're navigating to the folder(s) you want, are you long-pressing the folder so that the '+' button and the 'select all' checkbox appears in the top right portion of the screen? If you don't long-press, you're merely entering that folder and will never get the '+' button to add it to the list of folders to search.

I just fumbled around myself with trying to add a new folder, and it took me while to remember to long-press the folder, then hit the '+' button that appears.