Hi,
A Debian user reported that increasing LoginCookieValidity did not work for him. It turned out that his PHP's session.gc_maxlifetime setting got in the way and was shorter than this timeout, so the session got garbage collected earlier.
I think it should be documented at this option that the user needs to ensure that PHP's session.gc_maxlifetime is greater than the value of LoginCookieValidity.
I don't think it's necessary to fiddle with session.gc_maxlifetime as phpMyAdmin as this may adversely affect other applications running on the same host.
Yes we can document it, but why not add a warning on the main page when this happens? Not everyone reads the doc...
I added to documentation, implemented check for this situation in main.php and adjusted default SessionValidity to be same as default for session.gc_maxlifetime.