MobileJoomla has two plugins for device detection:
Mobile-Simple - really simple plugin that covers some of the most popular devices,
Mobile-TeraWURFL - plugin based on TeraWURFL library that is able to determine almost all existing mobile devices.
A work around is to disable the Mobile-TeraWURFL plugin and enable the Mobile-Simple plugin. That way the site will work for at least some visitors. Hopefully a better long term solution will be suggested.