So i’m looking into it more and from what I can tell your list of mobile browsers used to generate the .htaccess files is completely hardcoded into the wp-cache.php file.
I can’t understand exactly what is happening in the .htaccess file, but it seems like this is a recipe for disaster. It means that if the user agent strings set in wp-cache.php differ from the ones set in the options for WP-Mobile-Edition then those strings that are only in the Mobile Edition settings will effectively get ignored by whatever is happening in .htaccess.
I have a feeling this is what is causing the intermittent bugs we’ve been experiencing. When I try it with my iPhone it works fine because my iPhone user-agent is accounted for in Supercache. But when someone with one of the unsynced user-agents comes Supercache saves the mobile version of the site as a regular cache.
When you first added mobile support, did you just copy the default user-agents from wp-mobile-edition? If so you should at least update the list, as many have been added, notably the ‘Googlebot-Mobile’ user agent, which sounds like it might come by often to cause problems.
Ideally Supercache should recheck the saved list of mobile user agents from mobile-edition regularly to make sure they match. The .htaccess part of Supercache should be auto-generated from that list and the user shoudl be reminded to update their .htaccess if the lists dont’ match.
Hope this makes sense, any insight is very welcome.