It makes no difference whether I change channels with the keyboard or remote. The intermittent changes to the zoom setting still occur. There does not seem to be a clear pattern as to when it will happen. Occassionally the original channel will change zoom just before it switches to the new channel.
I have tried different resolutions through VGA and it makes no difference.I know that I am not the only one with this problem as there have been unsuccessful attempts to find a solution on Hack7MC.com here
It would seem perhaps that Microsoft have tried to be a bit cleverer than the Vista setup to automatically adjust zoom settings by reading flags from the video signal so that any attempt to apply manual changes to registry settings are not retained.
Why couldn't they have left a perfectly good setup alone?