There are some serious bugs in the template editing feature (introduced only recently) that will change your important Blog settings like date formats, comment moderation, etc whenever you edit and save your custom Blogger templates.
Here's a description of problem that I been seem to occur very often in the recent days:
1. While editing a template, if you preview the changes two or three times and then save the template, it will internally modify the blog archive settings such that the "Enable Post Pages" setting will be switched off. That means all your permanent URLs will be gone.
2. The above bug also modifies the Archive Index Date Format that you generally see on the right sidebar of this blog.
3. Today, it was worse. I made a small change in the blog template and it completely ruined by Comment settings. Almost all the values were toggled including the "Enable Comment Moderation" setting.
While I don't have steps to reproduce the above problems, they keep happening whenever I change my templates. So make sure you are not facing similar issues - always double check your old Comment and Archive settings whenever you change the blog templates.
Google spent so much money in acquiring Youtube, I wish they could spare some funds for making Blogger secure, stable and free of these "dangerous" bugs.
Related Reading: Blogger Templates