I was checking my reservation for a one-way BWI-MSP-SEA economy award ticket on Delta.com earlier today, and when I clicked on the seatmap for the BWI-MSP leg (not on the MSP-SEA flight though) it shows my seat assignment, but there's a window at the top of the screen that says something along the lines of my seat can't be assigned, and that it'll be settled at the airport. When I click the "x" to clear the message though, the website redirects me to the Delta home page.

Here's to hoping this is just a bug and hasn't affected my reservation in any way.