Booked a r/t award ticket, non-stop each way < 700 miles. Outbound in IN (saver F), return in XN (saver econ.). The receipt says:
The return should be 10,000 miles, but I was charged 37,500 miles r/t. Had I booked two one-ways it would have been 2500 miles cheaper. The MP agent says that the 10,000 mile price does not apply when the return is not in economy, but cannot tell me why. She also told me the 700 mile thing is a "promotion".

I would just cancel and re-book, but one of the flights is no longer available.

Update: The agent talked to a supervisor who supposedly would be able to credit the 2500 miles, but that he would have to wait 1 hour or more to talk to a MileagePlus agent. The agent said the supervisor would email me when he was done.

Update 2: A 2,500 mile adjustment appeared in my account! ^