Originally Posted by tomsem
After an update, Kindle will usually re-index all of the content. this takes system resources, and performance will be sluggish, and it is more vulnerable to runtime errors that cause rebooting. I've also seen situations where it seemed that there was a memory or resource leak resulting from running certain Active Content apps. And rebooting problems seem to be more common when a new device is shipped. Those are usually addressed in subsequent updates.
My Kindle came with the latest firmware. It has 6 books on it and no active content. It just auto rebooted when I went to change the light settings. Hasn't done it again since the first time but others have mention auto rebooting so I know I'm not aone. I think it's the firmware's way of dealing with problems. Never had this issue on any other Kindle.