Change the vncconfig line to include SendPrimary=0 (e.g. vncconfig SendPrimary=0 –nowin &)
Restart your VNC sessions
How it works:
vncconfig is a program that manages shared functionality between the x11 server and your VNC session, most notably shared clipboard functionality. Without this running in the background, you cannot share a clipboard.
X11 maintains a concept of a “primary” buffer (for selected text) and a “clipboard” buffer
SendPrimary defaults to 1 (on) which instructs vncconfig to send the primary (selection) buffer to the clipboard buffer, in effect overwriting anything there