This works well except for the header image. I have chosen twentythirteen for the mobile theme and a child version of it for desktop, with the header image full width on desktop and just the left side of this image on the mobile version. Switching between themes on the desktop confirms that the image settings are correctly saved as I move between them.
However, using the mobile it picks up the header image from the desktop theme. The only option I can think of at the moment is to hack the header a lot, which is a shame because twentythirteen is otherwise mobile-ready.
Do you have any ideas please? The draft site I'm just setting up is http://www.interweave-now.org.uk/ednabike/wp/.
Thanks very much