The vncviewer will crash on a multi monitor client if the positions of the monitors are switched. For example:
* Start out with HDMI1 left of HDMI2, login to create a new session.
* Switch positions with: xrandr --output HDMI2 --left-of HDMI1
I also observed the crash when creating a session in non-fullscreen non-multimonitor, then changing positions, then activating fullscreen over all monitors.
*** This bug has been marked as a duplicate of bug 4516 ***