Randomly expired session cookies

Hi! We are getting weird behaviour from PHP function session_start(). More or less randomly, the cookie expired date is in the past, something like "expires=Wed, 30-Apr-1902 10:05:03 GMT". (As it happens, this is very closely twice the current time in seconds since the epoch, if you do some signed/unsigned conversion.) This keeps happening on two systems with different versions of PHP4, Apache and Red Hat Linux. The problem seems to be load-related, because it disappears on weekends. Graceful restart helps temporarily. Has anyone heard of something like this? -- Ari-Pekka Tingander Song Networks, Finland