As far as I understand it, ditto blocks were only used if the corruption was detected due to checksum mismatch. If the checksum was correct, but metadata turned

As far as I understand it, ditto blocks were only used if the corruption was detected due to checksum mismatch. If the checksum was correct, but metadata turned out to be unusable later (say because it was corrupted in memory, and the the checksum was computed after the corruption happened), that was treated as a fatal error.