I'm using WPMP on a site where we're defining the COOKIEPATH and COOKIE_DOMAIN constants manuallysubdomains. Unfortunately WPMP doesn't use these constants when setting the switcher cookie and therefore the cookie doesn't work correctly.
I've modified the wpmp_switcher_set_cookie() function in the WPMP Mobile Switcher plugin so it works correctly. The setcookie() line in the function now reads:
setcookie(WPMP_SWITCHER_COOKIE_VAR, $type, time()+60*60*24*365, COOKIEPATH, COOKIE_DOMAIN);
It'd be great if this could be implemented in the plugin.