have to bow out here since I no nothing about Mac server software. If I had to make a guess I would say that use of the function keys (CTRL, ALT, CMD etc are being blocked by the |Screen sharing element.
I have a remote desktop app on my iPhone that does exactly that. I can rd in to restart AwareIM if I need to but I can't press CTRL ALT DEL to bring up Task Manager unless I either buy the pro version or set up some macros to do it with one click.
Have you got space on your home machine to quickly install a V8 eval? If everyone's comments in this thread works - then you know for sure it's either the screen saver itself (most likely) or something in the Mac Server software that is disallowing it