I am playing Solatorobo: Red the Hunter (which is a DS title) on my 3DS, and I often just shut the 3DS while I am walking around (thus suspending the game).
It seems, however, that I never manage to pick people up via StreetPass while I have a DS game suspended in my 3DS.
Is this actually the case? Is there something about suspending a DS game that prevents StreetPass from working? Or have I just been unlucky?