In Mobile View (either on my phone or on my laptop), when I click in the search box, the entire screen goes completely white...absolutely nothing shows on the screen. I can still type something, even though I cannot see what I am typing, but after I hit enter the search feature works correctly. I tested this here, at mediawiki.org, and it does ALMOST the same thing....the page goes blank except for the search box. It is definitely better on mediawiki.org than on the site I am working on, but I would still consider it a bug in the code.
Topic on Extension talk:MobileFrontend
Have you tested using other mobile devices, or at least with a different browser on the same device? What happens if you try the mobile view with a desktop system?