I don't think that yours is broken. My '06 Nismo operated exactly that way from the time I took delivery; my current '16 does the same and IIRC, Nissan does spell it out a little more clearly in the '16 OM than in the '06. I found out pretty much the same way you did; sucking in fumes when on the floor setting. I just got used to setting on recirc when needed and then switching between floor when I wanted heat and face when I wanted to stop outside odors. Back when they were new I seem to recall some chat on the forum about it. Nobody knew the reason for it but it wasn't uncommon among manufacturers.