I forgot to mention, that i'm not using any emulation software like Parallels to run windows on the macbook . WinXP is running natively on the mac hardware (i used BootCamp to setup a dual-boot configuration)

Is there maybe a problem, that the SHIFT key sent by the Desktop-PC-keyclone is not properly interpreted by the Macbook-keyclone and therefore ignored?

Furhtermore, when i was holding down e.g. SHIFT-s on my Desktop-machine, a sequence of captial 'S' was outputted on my desktop-notepad
and a corresponding sequence of small 's' letters was outputted on my 'remote' notepad, EXCEPT a captial 'S' now and then

Desktop: SSSSSSSSSSSSSSSSSSSSSSSSSSSSSS...
Remote: sssssssssssssssssSssssssSssssss...

That was the moment i got totally confused and rejected my "illegal SHIFT-key code"-hypothesis