Ah ha! More info. So I wanted to fit my new super cap, but first I wanted to check my Mobius was talking to my PC, as I'm cautious like that. I couldn't get it to talk.
Now I know it works, it's been working just fine. So I went through my different mini-usb cables and found that different cables did different things with my Mobius. I have different mount/dismount noises on my PC. (A female voice saying "I'm ready" and "Thank you", respectively, since you wondered. It freaks out people when they first hear it.
) Anyway, I got all kinds of random mount/dismount noises with some cables, so I think the cables may be a variable too.
Anyway I found a cable that worked okay, did my work, checked it still worked, updated the firmware, checked it still worked, formatted my new Integral 64GB card on my PC and checked it was found on the Mobius then formatted it in the Mobius. Yay!
A bit of a faff, but hopefully with the new firmware, the memory card issues will no longer be issues. I reckon it's worth having a few data cables to try on uncooperative Mobius units, though.