If the RDP Keep-Alive feature is enabled on a Windows Server 2008 (or Windows Server 2008 R2) server, manually stopping the Remote Desktop Services service (Windows Server 2008 R2) or Terminal Services service (Windows Server 2008) will leave the server in an unstable state: restarting the service will not re-enable RDP functionality, and the server will hang during shutdown.
The keep-alive thread is started by the Remote Desktop Services (Terminal Services) service if Keep-Alive is enabled, however it runs in Kernel mode and can therefore not be terminated automatically when the service stops.
Do not attempt to stop or restart the Remote Desktop Services (Terminal Services) service if the RDP keep-alive mechanism is enabled.
When Keep-Alive is enabled and the Remote Desktop Services (Terminal Services) service is stopped, its svchost.exe process will remain in the Task list, even though the service is reported to have stopped correctly. When the service is started again, a new svchost.exe will be started however the server will not accept incoming RDP connections due to inconsistency in the TermDD driver state.
The Keep-Alive feature can be enabled by Group Policy:
Windows Server 2008 R2: Computer Configuration\Administrative Templates\Windows Components\Remote Desktop Services\Remote Desktop Session Host\Connections