Don't know if this is a bug...but sure seems like it.

When looking at itineraries shortly before check-in I will sometimes click on "Change Flights" just to see if there are any desirable options offered. Almost always I get a message like "this cannot be done online" or something such.

(Pre-apology for doing a comparison to NWA)

Back in the day, this was very easy on NWA - oftentimes the change of flights involved more $$ than I would think about - but it was at least very easy to click and see my options. No big deal. And sometimes there were great options available at no charge. (I was WorldPerks gold at the time.)

Somehow I never even get to the point of even seeing any options available with delta.com.

(But please don't work on this until you get the award calendar working...first things first haha!)