Icedragon, I had a similar experience with a book of Christmas carols. My mother and I both play the piano and have had the same carol book for my entire life. Every single Christmas, out comes the carol book, one of us plays the carols, we all have a sing-song, away goes the book.
Last year, we both suddenly realised that one of the pictures in the book had mysteriously changed. The illustration accompanying the carol "Good King Wenceslas" was so imprinted on both of our memories that we were shocked to find that it now looked completely different.
My Dad, being Mr. Logic, said that couldn't possibly have happened but was puzzled because we were both saying the same thing. He made us both independently draw a rough sketch of the original image as we remembered it and we compared them. They were roughly the same. Mum and I both (without seeing the other's drawing) drew an image where the figure of the King was looking out of a leaded window on the right, and the servant was to the left trudging through the snow carrying a dead goose, with a forest behind him. The image that was now in the book, looks nothing like the image we both drew - the figures are in different places and there's no window...
We were both so affected by this strange turn of events that we haven't played any carols since... My Mum, in particular, doesn't even want to open the book. We're all at a loss as to what happened so I understand your frustration!