> Unfortunately. Thumbs plus doesn't recognize these drives until you close the program and restart it.
Just press Ctrl-F5 to refresh the tree.
> At that point, I can access it with thumbs plus as normal. I can even assign a volume alias to the card. But if I remove the card, I would have expected to see it listed as an offline disk, but it's not there.
Did the card have a distinctive volume label (not volume alias)? If not, you can assign one from within ThumbsPlus by right-clicking on the drive and using 'Label disk'.
If you have made thumbnails for files on that card, it should show under Offline Disk when you remove it and refresh the tree.