Aha! Every once in a while, when I fiddle with my template (adding a link, etc.) somehow the "Save Changes" doesn't quite do the job. This time I found that one of the HTML tag brackets had been replaced by its escape characters, which made the rest of the page choke the browser, even though it was all there when viewing the source...
Thankfully I avoided having to build my template again from scratch, like last time.
Feh.
