I'm also having this issue.
Mobile users were seeing the cached desktop page (which didn't include the option to display the mobile version)..
And if a mobile user had been the first to visit a page, a desktop user who then visited it would see the cached WPTouch version of the page.
I decided I would have to disable Wordfence caching till a solution was delivered.
But then I found the following bypass setting would work:
If the User-Agent contains (without quotes): "iPhone" then don't cache it.
It looks like this would work for mobile devices (smartphones) in general:
If the User-Agent contains (without quotes): "Mobile" then don't cache it.
I'm fairly sure this is a recent problem, perhaps caused by a recent change to WPTouch or Wordfence.
It would be good if there were a way to cache the mobile pages as well.