When I went to the page where I change my preferences to see what could be configured and subsequently tried to log out, bugzilla passed to me a set of cookies each with an expiration dates somewhere in 1969! The result was that I could not successfully logout. bugzilla then reported to me that it had lost track of me and that I would have to log in again to do anything.
This does not seem to be causing any trouble on our end. The reasoning that the date is set as such is that it automatically becomes an invalid cookie upon bein set so when you relogin it will set the cookies to a valid state with 2029 as the expiration year.