Can't post image galleries on child pages

One of our webmasters recently discovered that he can't post image galleries on child pages anymore. Here is his blog:

Most of his images are under Photos - Week 1. However, you'll notice that the last page in the list, 7/30, simply redirects back to the parent page. If I change the page so that it has no parent (like 7/31), it will work again.

This has only been happening for a few days, and as you can see, the previous child pages are unaffected. We're using version 2.8.2.

Has anyone had a problem like this?