This is happening in the same document. This has happened on and off over the years, but I only asked this time round because it became an issue. My basic question is:

in what circumstances is text both tracked as an insertion and struck through when mark-up is showing? (I would have thought - and it's normally the case - that if I add text in mark-up, it's tracked in underline; then if I change my mind and delete that same text in mark-up it disappears rather than strike-through being added to the underline.)