Stumbled on a couple of seemingly related oddball bugs.
Create a new, empty project. Use Minimal, and make sure that Use thumbnail for folder icon is chosen. Add a single webloc, something that will automatically grab an image (like https://jgromit.com). That single object has the "heart" symbol on it, but the Thumbnail box on the right remains blank, even with an F5 refresh. Only by closing and reopening the project do you finally see the chosen thumbnail. A very minor issue, to be sure.
But the related bug is weirder. I can't reproduce this at will, though I do have a couple of projects that show the error every time. If I choose a "webloc's only" project on the left, jAlbum opens it, and the Thumbnail box on the right is showing the correct image. But now if I open a different "webloc's only" project from the left, the thumbnail image from the first project is still showing, even though that thumbnail image isn't even present in the second project. A quick close and re-open (CTRL-W, CTRL-1), and everything's fine again.
None of this seems to have any effect on album creation - it appears to be purely a display issue.