Thanks to StefanL in the ooforum.org, I can now mix landscape and portrait pages in the same document. (Quite why this should be news is a matter for another day)
To follow StefanL’s suggestions:
- Open the Stylist (F11).
- Chose page styles (forth icon from left).
- Right click on any style: “New”
- Give a new name to this page style and use this style for your landscape settings.