RDP Client hanging at "Securing remote Session"

Hi Forum,

I running an RDP Client on W2k8R2 machine - when connecting to target machines higher than W2k8 the RDP Client hangs for about 30 seconds at "securing your Session".
At network dumps I see that the client is asking "ctldl.windowsupdate.com" getting back the IP and trying to connect at TCP/80. The guy seems search for some updatestuff..
The firewall is configured to drop the packages instead of rejecting them - which is causing the 30 seconds delay.

To fix the rootcause - how to disable this update behavior? Seems to have something to do with new implemented rdp certificate authentication?

Thanks for your help in advance,

Andreas