I tried what you suggested. The problem seems to be specific to this book. I've tried some others in this series (all split from one mega-book) and they don't work also.
If I edit metadata on an empty book, it works fine, but it won't my book. There is a lot of data in the opf file that seems to have come from the original book metadata plus from the Sigil split.
Should I just start a new opf file and copy the info I want into the new file? As I mentioned, I'm not techie so a quick fix would be fine for me. Also, I could create a 'master' opf for the whole series.
I have Windows Vista