With a favorite list created for my wife, and then one for my 2 kids, it also got a little confusing here at first.
However, in ref to "it has re-set itself several times", that's not the case. The guide changes because someone hit the "Guide" button while in guide.
They probably did the same thing I find myself doing sometimes, i.e., I'll hit the guide button to get out of guide, and then hit the cancel button to get out of guide, but I'm already on the next guide when I exit. A bad habit from using other buttons, like "INFO", which if you keep hitting will eventually exit from info.
I finally got my wife and kids (and me) to look at the top when they press the guide button to make sure they have what they want, and if not, to keep hitting the guide button until it has the right menu.
Edit: Later on after this post, I remembered another mistake I also make on the guide list when it happened again. Without ever looking at the remote, I'll hit the guide button to go into guide, then when I want to page down, I'll accidently hit the guide button instead of the page-down button and go to a different guide.