We're on ZCS 4.5.11 (we won't be upgrading to 5.x until we get a few large projects out of the way, but our TEST instance is on 5.0.9 as of last week).
This is an unusual problem on our PRODUCTION system and it's not reproducible, but I've seen it with my own eyes. Ever since our enterprise was forced to upgrade client browsers to IE7, I've had various users call saying that they are unceremoniously thrown back to the login page for no obvious reason. Sometimes they're just reading mail and not clicking on anything. Other times they are doing something normal like changing to a different mail folder or deleting a message. Sometimes they can't even log into ZCS at all, they just keep getting dumped back to the login page. The only fix that my support techs are certain about is the laborious process of re-installing IE7 on the machines with this problem. But that's only temporary as the problem usually returns at a later date.
This morning, I wondered whether or not this was related to themes because we've had a few issues with those in the past and have at this point resorted to telling users to only use the Sand theme for now. So I had a user who was unable to log in this morning. I logged into her account on my workstation with no problem (Linux/Firefox 2.x). I logged into my account on her workstation with no problem (Windows XP/IE7 and the Steel Theme in my account). So when I was logged into her account, I changed her theme to Sand and told her to stick with it. Everything seemed to be OK again. She was able to log in, and access her mail. But, a few minutes later she called back to let me know that she got dumped out again while just reading a message and not actually doing anything with the interface at all. She hasn't changed the theme. So that was a dead end.
Has anyone else experienced this?