Post-merger seat selection

After a couple of weeks away from air travel (road trip via RV - 3500 miles, 16 states and lots of fun), I am back to the airports.

Now that the DL/NW merger is advancing, there are still some areas that do not work correctly. I recently booked flights up to Chicago, via delta.com. The site booked me on DL numbered flights, but operated by NW. When my upgrades came through, I went to delta.com and selected my normal window seats.
Surprise, surprise, when I checked in (directed to NWA.com from delta.com), my seat changes had not been processed :-(.

Lesson learned: when travelling on NW operated flights, be sure to make your seat selections at their site.