fe_user cookie expiry date is not affected by $TYPO3_CONF_VARS['FE']['lifetime']
We are currently running a TYPO3 installation for a customer which holds a page mainly devoted to a forum.
This forum is used as a support forum for teachers, and thus users and moderators may take a long time to compose posts.
However if they do not browse the page otherwise during a time longer than one hour, they get logged out and lose the text. This is an issue mainly in IE, as Firefox does not care so much about the expiry date.
However I tried to increase the cookie lifetime by various means, mainly php values (in a .htaccess) with no effect.
The cookie lifetime is stubborn at 3600s.
After some research in tslib_fe, tslib_feuserauth etc., I found that the cookie lifetime is controlled over $TYPO3_CONF_VARS['FE']['lifetime'].
When I increase the value however the cookie expiry date did not change.
I am currently at a loss how this cookie does not respond to any of my changes and require some help with that.
(issue imported from #M15785)