Expiration time of submission token for new threads (and possibly other forms)

Yesterday (or two or three days ago, I do not remember when exactly) I logged in to LQ, with the "remember me" feature active.

In this session, I have started two threads. For one of these threads, I started to write a post. I did not submit it, just previewed what I have wrote so far a few times. Until yesterday, it worked fine. A few minutes ago, after I woke up, I previewed that post again.

The surprise result:

LinuxQuestions.org Message Your submission could not be processed because the token has expired. Please push the back button and reload the previous window.

It should not happen, right? My session is stil active and working, as I confirmed by reloading the other tab. The preview button generated yesterday should work now too, I think. But it does not.