Hello, all. We've seen this bug rarely but enough to know that it is a real bug and not just a coincidence. Here is the report from our internal trouble ticket. Unfortunately, it smells like it might be something in the NX libraries:
The user called because she could not see her mouse cursor in her virtual desktop. It was visible in her physical desktop. As we later observed, it was indeed present in the virtual desktop, e.g., if she happened to stop the mouse over a file in Konqueror, it would display the thumbnail, but the mouse cursor was not visible.
We tried suspending and reconnecting; that did not work. I could see where the mouse was supposed to be via my VNC session to her physical desktop so I tried to change the mouse cursor theme but that did not work (and required a restart of KDE).
Finally, before rebooting to try to re-establish the connection between her physical and virtual desktops to display the mouse cursor, we thought to suspend her X2Go session and then completely close her X2Go client. When she restarted the client and reconnected to her X2Go session, the mouse had re-appeared. We did not need to reboot the physical computer.