Possible that your neighbor has his remote code set to the same as yours? See if changing your remote code fixes the channel changing on its own....
I did think of that as the neighbor a couple doors down does have a couple 605s, and a 630; so that could be the problem but he is at least 80 feet away.
(I helped him with his install but didn't do the recievers - he activated them and I don't know if he "paired" all of his remotes. See the link below if you want to read that saga.)
Anyway, my Mom said (when I talked to her this morning)it didn't happen again last night after I had her power the 630 down (disconnecting the power cord), and wait half an hour before powering it up and then trying it => after letting it sit re-powered for another half an hour.
We'll have to see how it acts next time we are at The Cabin as she's coming home today.