WordPress itself change the file permission of wp-config ?

I tried to change the file permission of wp-config.php to 400 or 600 but after change it using file manager of cPanel the permission is always set back to 640. I found the following post that says “Some web hosts won’t allow you to make certain permisison changes.”

http://wordpress.org/support/topic/wp-configphp-15?replies=3

Although I could change other php files to 400 or 600, also I can change the wp-config permission to 440.

I asked to the host about this and received following answer;

Yes WordPress can and will change the file permission on that file to a permission that it needs in order for the dashboard to access that folder.

Wordpress files are run as your cPanel user, so they would have the ability to modify your file permissions without you actually changing them yourself. As for your recomendation from that article that was provided, we would not modify any file permissions without notifying you beforehand. We would not be making these changes on our side. This issue appears to be a wordpress specific one. You should reach out to the wordpress community for further assistance with this issue.

Any idea why I can’t change the permission to 400 or 600?
Does WordPress itself change the permission of wp-conig?

My setup is like as follows

The host: inMotion
WordPress version : 3.6.1
Plugins: Akismet, Contact form7, Really Simple CAPTCHA, WP Multibyte Patch
installation location: html_public root and sub-directory (two site: same issue)