“Fun” with logins

I started missing Linux on desktop, so due to 256MB memory went with Xubuntu couple of days ago. I’m going to skip issues with network card and kernels in this post though.
The case is that when I choose to switch user, then.. well it switches just fine, that is it gives login screen for another user. But, when another user logs out, login screen won’t appear. Can you guess what happens instead? My desktop is shown. Fully functional. No need to authenticate at all. Even if I have thunar (xfce’s file browser) opened with root privileges. Here goes the famous linux security.. well it’s an exception to that, I guess. Like the one with ssh keys some time ago.
Any way, there’s a thread on ubuntuforums.org about a similar issue, so I thought I’d reply. Except that I can’t. At first I couldn’t log in, then when I got in, I get logged out every time I try to post! No, my cookie-handling is fine. Turning off firewall, clearing browser cache and switching browser to a different one as some usual things to try when experiencing something odd in networking, don’t help.
Interestingly traceroute to forums never completes. It goes on forever with *** after gw0-0-gr.canonical.com [] hop. With my connection, that is. Traceroute using another connection shows that this hop should be right before the destination.
Might be a faulty ip perhaps? I did get one that was in ahbl blacklist as an open proxy some time ago and needed to acquire new one to have access to mozilla irc channels. Disconnecting modem power didn’t get me new ip this time and I really don’t feel like dealing with my isp’s tech support. So I hope it clears by tomorrow all by itself (well maybe disconnecting modem for night). But if it doesn’t, I still have to deal with it, ugh. I don’t know too much about networking, certainly not about networking issues. Fingers crossed here.