Someone reported that WordPress at boku.ru hasn’t been remembering the name and email which you enter in comments. I vaguely remembered this working before. After some investigation, turns out it was W3 Total Cache plugin which uses comment_cookie_lifetime filter to drop standard WordPress cookie lifetime from half a year to 30 minutes. And since my site runs as GMT, this was eaten by the 4-hour time difference.
W3 Total Cache did that because for cookie-less visitors it serves fast static version of the page (which can not be tailored for each visitor and have their name pre-entered, the way names are handled now). As long as you have posted a comment, you receive a cookie and WordPress serves you slower, dynamic version of the page. So the longer the cookie lifetime is, the longer you’re going to be served dynamic pages (but the longer your settings are going to be preserved).
This setting can be changed at “Performance > Page Cache > Advanced > Comment cookie lifetime”.
If you’ve stumbled upon this post while solving a related problem, here’s some additional pointers:
1. WordPress stores commenter name/email/url in cookies:
comment_author_*
comment_author_email_*
comment_author_url_*
An example of how querying for these values should look like is in /wp-includes/comment-template.php/comments_template()
2. Your comment form is generated either by this, or by customization hook in your theme’s comments.php.
3. To debug cookies, add print_r($_COOKIES); to your theme’s header.php, don’t forget to remove it later. Use Wireshark or your browser’s request sniffer to track what’s being sent.