Currently, TLF (or rather EditManager.as) treats shift-enter as a regular return unless the context is in a ListElement. When the context is a ListElement, it does not create a new list item, but it does create a new paragraph.
The general convention in applications is that shift-enter is used for a soft return which inserts a line break without creating a new paragraph. I think EditManager should do the same. I will be happy to make this change if folks agree with me… Harbs