Last modified: 2014-02-12 23:55:25 UTC
It became impossible after beta was activated by default.
Works for me with the opt-in cookie cleared from my browser + $wgMFConfigProperties = array( 'isBetaGroupMember' => false ); in LocalSettings.php, but otherwise there does not seem to be a way to get out of the 'beta'. However, this might be design since the beta style is becoming the default style.
Just poking this - Max, is this still a problem for you?