This seems to be a common issue for people using the built-in Ubuntu remote desktop server, vino, and the proprietary Nvidia drivers along with compiz visual effects; whereby the remote desktop screen on the VNC client fails to update unless you reconnect to the server. There seem to be plenty of bugs lying around open for this issue and it seems to affect a range of VNC servers (it doesn't impact TightVNC from my experience) a work around is as follows:
1) Open a terminal run: gconf-editor
2) Go to /desktop/gnome/remote_access and enable "disable_xdamage"
3) I then had to reboot to make the changes take effect, there must be an easier way to restart the vino server on display:0 but this was quicker than searching for the answer!