Why has knoppix (on hard drive) done a re-login shortly after resume from Suspend?

[winger9]

I had put knoppix into Suspend (Fn+F4) for a few minutes (which I've done many
times before), and then pressed SPACEBAR to resume it. It resumed and displayed
what was on the screen previously.

I didn't type anything but proceeded to read the text that was in a Kate window
that was still open from before the Suspend.

However, about 20 to 40 seconds after the resume-from-Suspend (as I was reading
the Kate text), the laptop appeared to perform a re-login (all by itself). That
is, it seemed to do the same as when you select KMenu/Logout/Logout. The
applications that I had open all disappeared, and a fresh Desktop was displayed
(the system uses LXDE).

The applications that I had open (before the re-login) were three instances of
the Chromium browser, and 2 instances of the Kate editor. I've had no problems
before by having three instances of Chromium open.

At the time the re-login happened, I wasn't doing anything or touching anything,
and the internet WASN'T connected.

I'm not sure if this re-login occurrence has happened before, but it's worrying
because if I'd had something important running at the time, then it would have
been disastrous.

Please could you tell me why the system would do a re-login all by itself, and
how can I stop it happening again. Thanks.

[winger9]

I forgot to mention:

The knoppix version is 7.0.2 (DVD).
The kernel version is 3.3.7.