FYI, I read all of the code that mentions 'lastupdate' and could not find where that field is being overwritten. The only place that updates that field includes punctuation in it and selecting the field from the DB also includes punctuation but it is often displayed (edit your home node) w/o punctuation so something is overwriting it after it is read from the database (which would cause it to be updated in the DB if the node got flushed to the DB later), but the code that does it appears to not mention 'lastupdate'.