OK, I wondered what was going on. I've purchased a book before from Kobo directly to the Vox, but I used the laptop tonight because of the sales. I had several pages open in the various discount categories, and it was just easier to use the laptop.
Oh, well, I do have the book anyway. In my Sony Library and ADE on the laptop, plus in Aldiko on the Vox, so I guess that's enough, eh?

I just wondered if something had gone wrong because I bought the book on the laptop and downloaded it there before opening the Vox Kobo library app.
Edited to add: I just put the Vox down, and the book has shown up on the Kobo list now with the download bar beside it. The site must be really overtaxed tonight.