../templates/j51_madison/htmlb] to [b]html-backup
I'm assuming you just mean /templates/j51_madison/html and that the "b's" in your reply are a typo?
First, I changed the name to html-backup and cleared my site's cache. The issue still existed when logged in as a super user.
Then I remembered that whenever I was logged in as a super user, a module using your J51ThumbsGallery module was appearing out of sorts. It's in position base-1b. Reason being, I had implemented the "Articles Anywhere" plugin in the module title in the backend, so that I could use an article in place of the normal title to fancy it up with an icon next to the title. It worked, so I left it that way. After your comment above, I disabled the module and my Zap Calendar issue went away. So, I replaced the articles anywhere reference with a normal module title. Tada! Thanks for your insight!
Keep up the great work! A very nice template.