Interesting. I just took the 16Gb card that didn't work, and put it in an HTC phone. I managed to format it OK in there. I then put it back in my Blade, and formatted it there. It seemed to be working. Then I put it in a PC, and copied files to it. It then stopped working again. I went round the whole cycle, and it's back in my Blade working OK. There's definitely something strange going on here.
Next up is to try to copy the files from my old card using USB cable with the new card in the phone, rather than putting the new card in a PC to do the copy...
Anyone got a good explanation for this behaviour?
I note that my 2G card isn't recognized as having valid partitions when plugged directly into my PC, but is when connected via the phone.
I had put this down to strange block-device wrapping of Android in that it doesn't really expose the full raw device, but the symptoms match what you describe.
I would say this is similar to the old LBA/CHS problem of the victorian age but it doesn't make sense for linearly addressed storage.
But... if keeping the device in the phone works - then do that!