SEP clients always download definitions from SEPM, bug?

Hi,

I have a policy for Live Update sin SEPM v11, now in SEPM v12 I have a problem where all clients download the virus definition form the SEPM and not from Symantec LiveUpdate servers.

Is this a bug? How do I prevent this from happening?
I want the clients to download content or virus definition only from Symantec Public LIve Update servers.

Many thanks
Oliver