I downloaded the docx file for Martin Noth's Exodus commentary from here to build a PBB, along with the initial cover image that was posted for it.
Later I noticed that a different more appropriate cover image was posted by someone else, so I downloaded that and saved it with the same filename as what I'd saved the first one under, replacing the first one.
I went to my Personal Books tool and rebuilt the book. It did not pick up the new image. I had to go back and click "Change" on the cover image and select the same file name over again in order to replace the image. It was apparently cached from before, even though the old file was gone.
Expect: Rebuilding a book should pick up cover image afresh rather than using cached one. Of if it's a question of caching being used to save time on the build, perhaps refresh the cover image if the file date is newer than when it was cached.
