Windows Update Isn't Listening

I was out of the office most of last week, traveling on business. My system has quite a few automated tasks that run, so I tend to leave it running even when I'm away. I returned to the office to find the system had rebooted, with a message that Windows Update had applied patches. There's just one problem: I don't use that option.Now, I know that Windows Update has an option to automatically download and apply patches at a particular time. I prefer to have Windows Update download the patches and let me choose the best time to apply them. Somehow, though, Windows forgot about my preference. It wasn't just a one-time exception, either; when I checked the Windows Update settings, it was set to apply patches automatically in the wee hours of the morning. The same thing happened on one of my test virtual machines, which also was set to download but not apply updates.

After some looking around over the weekend, I couldn't find that anyone else was having the problem. So I'll ask you. Has anyone else experienced this strange forced-switch in the Windows Update settings, on Vista or XP? I saw it on two Windows XP systems. The notebook I use while traveling had Vista. I had gone to the Windows Update site manually the day before I left to be sure everything was patched, and it still "remembered" that I wanted to install patches manually.