Boxcar Children, The: Mystery of the Hidden Beach, The - Is Jessie Schizophrenic?!
This slip-up is at the end of chapter six. On the next-to-last page of that chapter (page 71 in the paperback version), Jessie makes a comment about the mystery they're solving. On the next page, the very last paragraph of the chapter says that Jessie agrees with the comment by saying "So do I." Why would Jessie respond to her own comment?