It seems there is some sort of race condition. We are getting about a thousand hits a day on our site from iPhones and Android phones. I'm wondering if it is a race condition when garbage collection kicks in?
I've received 4 emails today from people on desktops that got served the mobile version of the site, and I've been doing tests on http://www.webpagetest.org for the last couple of days, and 4 times I've been served the mobile version of the site during a test.
I'm running the devel build from 7/10.