The Mac client has it. I did find out the hard way that the combination of Mac's VNC server and my client on Windows send a stream of press-and-release message

The Mac client has it. I did find out the hard way that the combination of Mac's VNC server and my client on Windows send a stream of press-and-release messages when I press and hold the space bar on the remote side. It took me a surprisingly long time to figure out what people where describing when I tried to speak.