OP, thanks for this very much. It will help out a lot of people.

But this is probably good for people that never get upgraded. There are definitely other combinations/sequences of events that will result in the box being unchecked without you realizing it.

So there are many of us that occasionally have this happen but I still haven't seen the pattern. It happened to me just this week for my flights this weekend. I checked all of my other itins and they were fine, so I have no idea why it was a problem on just this one.

Personally I think the easiest thing for DL IT to do to solve the issue is rather than having a "Request Upgrade" checkbox that is turned on by default but can sometimes get unchecked for some reason, there should be a "Decline Upgrade" box that is off by default. They could also have a "Are you sure you want to decline the upgrade? What are you stupid?" confirmation box too.

I think this would greatly reduce the number of times that people get mistakenly left off the upgrade list.