The Endurance Page cache plugin is a plugin activated automatically by Bluehost. It may cause your visitors to see the mobile theme on their desktop browsers and vice versa. To resolve the issue, please contact Bluehost and ask if they can configure the plugin to ignore the WPtouch Pro user agent list below.
You can then use the Power Pack extension to activate caching for the mobile theme. If Bluehost is unable to exclude the user agent list from the caching plugin, ask if they can deactivate it. After it has been deactivated, you can use the Power Pack extension to cache both the desktop and mobile themes. It will do so separately to help prevent caching issues.