This is with $wgMFAutodetectMobileView set to the default value of false.
With MobileFrontend enabled, clear the HTML cache. On a page, click the "Mobile view" link. The page you were on will load with the toggle URL (/index.php?title=Page1&mobileaction=toggle_view_mobile).
Now in the mobile view, click a link on that page to go to another page. The second page (and subsequent pages) will load in mobile view at the normal URL (/wiki/Page2) and will be cached in mobile view.
The file cache should be disabled if a page is being loaded in mobile view.