You are doing nothing wrong. Sitepoint must be setting the cookie to expire after a short period of time. Many times I have been writing a post, click to submit it, discover I was no longer logged in, then hit the back button to go back to find my entire post is gone. Infuriating! A longer post can take some time to write, plus other distractions. What I learned to do is copy my post content into a Notepad file before submitting so if my cookie expired, I won’t lose everything I wrote.