Buying tickets, no...you can buy tix any way you want. Traveling on them is what I'm talking about. Also, when you check in at the counter your itinerary comes up. What the agent sees on your departing itinerary with a round trip ticket is the WHOLE itinerary, including the return. It's all under one record locator. Since the one-ways are one-ways and in essence purchased separately under separate itineraries, they each have their own record locator. So when you produce your ID and they pull up your record locator they only see the outbound, one-way ticket. Thus the possible flag.

I hope I'm not confusing anyone, I'm starting to confuse myself. More coffee?