This symptom first showed up in one of my solution files when it was converted from FMP 9 to FMP12. I traced it eventually to a container field whose content (photo) was replaced by another photo without first selecting "Clear" from the edit menu. Like you, I tried recovering a recovered file and have been testing it for more than 3 months without issue. I know this is not advisable but so far, so good. My thinking is I would not be able to recover the file in the future if anything else untoward happens to it.