When I have webadmin opened and session expires (or not... it takes only about 5 minutes) and I click any link I get 404 page instead of redirect to login page (version 1.4.25).
Which screen are you in? I cannot reproduce it. I tried on my local and set my session timeout to 60 secs in admin general settings. Then if you don't do anything, it will redirect to login page. If I click somewhere else before the redirect, it also goes to login page with url http://127.0.0.1:7080/login.php?timedout=1