(RC15) Front/Back Matter -- More detailed description please

What do I have to set so that reciprocal pages are displayed?

If you right-click on the Front Matter or Back Matter folder in the binder, under Section Types you can set the appropriate type for Default Subdocument Type. So setting the default subdocument type for your Front Matter folder to “Front Matter” will cause all items within that folder to use the “Front Matter” type if they are set to structure-based. If they have had some other type manually applied, the default subdocument type will not affect them.