Book cover defaulting to a blank pixel

I’ve started using the bookshelves feature to track my reading. I’ve added a book to my currently reading bookshelf, and made that bookshelf appear on one of my pages.
However, the cover image always shows as a blank 1x1 image on the page.

Is it something I’m doing wrong? Or has maybe the book not got a cover that can find?

For reference, the book is Harry Potter and the Philosophers Stone, and the exact ISBN number of my edition is 9780747532699.

Behind the scenes, the cover art is fetched from ISBNdb for that specific ISBN. Searching for the book there reveals the missing cover art. I don’t know the specifics of @manton’s implementation, but sometimes cover art is fetched from Open Library instead.

Hopefully, it will be possible to manually set the cover art in the future. Until then, you can work around the problem by using the ISBN for another book edition. For example, 9781856134033 should work in this case.