Thanks to everyone for the responses. I'll chalk this up under the "you learn something new everyday" category.

Here's a follow-up question. In this type of scenario, let's say that there's a major schedule change on the DL portion of the itinerary. Who would be responsible for addressing the situation if I wanted flights that better matched the original itinerary? For example, in the past I've booked US codeshare flights through UA. When I had schedule problems, I always had to go back to UA because they were the ones that issued the tickets. Of course, that situation was a little different, in that US & UA were partners, and UA and DL are not.