WP image gallery won't page through full images

Just uploaded 22 (small <100KB) to the WP built-in gallery. The thumbnail display looks fine in the post, and the first image displays as full page OK, but the Next–> button does not work correctly. Instead of displaying the next image full page, I get display of the full gallery thumbnails & see this same problem when I click on any other image thumbnail in my post. The first time I uploaded the images into a new post via Create Gallery.

When I saw the problem, I deleted the gallery, then created a new gallery using the same 22 images but from the media library: same behavior. The image IDs seem correct. The gallery is in this post:

http://ptartist.com/scanned-pages-of-the-second-edition/

[gallery columns="2" ids="1629,1630,1631,1632,1633,1634,1635,1636,1637,1638,1639,1640,1641,1642,1643,1644,1645,1646,1647,1648,1651,1650"]

I looked at some older posts with galleries (that may have worked previously, but not sure that I paged through them). When I page through another gallery with 15 images it is also broken, I can only page 1 or 2 images as if it was a 2 image gallery, one links to a blank page, etc.

Is this a 3.8 problem?