There's a problem booking reward flights and mixing classes.
I chose "I want to break my journey and choose my stopovers" and try to book XXX-LHR-YYY with the connecting flight XXX-LHR in economy and LHR-YYY in First I get this message
Error
•Sorry, we cannot currently book the journey you have chosen. You may wish to reselect a different cabin, try again later, or call your service center.
(this has worked fine before)
If instead I choose
No, I want to continue without stopovers
there's no problem (I'll be booked into Club Europe on the connecting flights, which I don't want)