WordPress Automatic Upgrade and Default Theme

Last few weeks, I worked on a WordPress theme design. But, it was the first time I used default as its theme folder. If you use WordPress, you might know how WordPress will deal with default theme folder. It will be used if something goes wrong with the theme. For example, you’re working on a theme file, and it’s broken, your WordPress theme will be automatically reverted to the default folder.
I chose to use default folder because I always want to have this theme loaded. But, I found that it was not the best decision to make. Why?
It’s about WordPress automatic upgrade feature. When WordPress 2.7.1 was available, I upgraded using its web-based upgrade system. Click on the automatic ugprade button, and voila! Latest version was installed. BUT, it will overwrite my theme files, which are located in the default theme folder. Luckily, I still have the backup. So, I re-uploaded the theme files into different theme folder.