Hi, once upon a time wordpress mobile pack had a specific file loaded by hyper cache (me and them agree on how to do it) so the detection was made by wp mobile pack. From version 2.x of wordpress mobile pack that file is no more there.
WordPress has no ways to detect the mobile device and share this information between plugins. Since hyper cache msut be the first to detect mobile devices and return a page if cached, or wp mobile pack create a file with a detection method to be used by hyper cache or is almost impossible to sync the detection. More probably wp mobile pack detect even the very old devices while hyper cache provide only two separated cache for mobile and desktop without distinction between mobile devices.
Probably you should not use a cache system… or try to contact the wp mobile pack authors and ask them how you should integrate their plugin with a cache plugin. I’m available for modifications to hyper cache, of course.