NWBC 5.0 PL-7, RDP-session, open NWBC and SAP-appl., RDP-disconnect, and RDP-connect, NWBC-session is lost

problem:

client-session with RDP to WinServer2008R2-64bit

start NWBC, logon to SAP-system, open application, edit some screen,

disconnect RDP-session

.... after a while ... some minutes (no timeout situation)

logon again to (the before disconnected) RDP-session

the NWBC screen is blank, the (before) opened sap-application is not visible,

only blank NWBC, SAP-session is lost. User has to logon to sap-appl. again. !?

the only chance is to kill NWBC, and start all over again ?

all other windows-application did not have such behaviour.

why NWBC ?