Mobile pages occasionally being served to desktop

Hi,

99% of the time, this app works great, but occassionally however a mobile page will get served to desktop, and vice versa.

Every time this happens I have to clear the cache using W3 Total Cache, and it then corrects itself.

Is there any reason why this keeps happening?

Thanks,

Chirs.

http://wordpress.org/plugins/any-mobile-theme-switcher/