This ticket was booked directly as an MFU - it never existed as something before the upgrade. My understanding in that scenario is the underlying bucket - the fare upgraded from - is a reward bucket (P?) which are fully flex, so the fully flex terms should persist through the upgrade and allow me to change. It shows in MMB as selling class U (ie redemption) for both the LH flight and the SH feeder flight, but presumably that is the current, upgraded bucket. There doesn't seem to be a way to tell what the underlying fare bucket was.

The kicker here seems to be the non-MFU leg of the journey. The flights on that show T for the LH and B for the SH, which definitely aren't redemption buckets. Shouldn't those have booked into P as well, or is that an indication of what the underlying buckets for the upgraded leg were? If that's so, then why is it not charging me to change that half of the journey too?

The two things that burn me up are A: I was only shown T&Cs relating to the P/U fares during booking - there was no indication that any other T&Cs applied to any part of the journey. And B: there is no way to see those T&Cs now. On previous bookings they've been both visible clearly in MMB and delivered in a big ugly text email but I've received neither for this booking. And C: It seems to be basing the T&Cs for the entire revised journey on the T&Cs for the T/B flights and ignoring the U. Okay that's three. Three things that get my goat.

Still haven't actually done the deed yet...