OK - so I had already followed the steps suggested by Hein Zelle here (https://bugs.launchpad.net/ubuntu/+source/nvidia-graphics-drivers-180/+bug/553415), which initially didn't appear to work. But the crucial bit, as Jerry said, was to reboot the machine. On turning on my PC this morning the motif problem is fixed. So I didn't need to use Jerry's reposted patch in the end.
OK - so I had already followed the steps suggested by Hein Zelle here (https:/ /bugs.launchpad .net/ubuntu/ +source/ nvidia- graphics- drivers- 180/+bug/ 553415), which initially didn't appear to work. But the crucial bit, as Jerry said, was to reboot the machine. On turning on my PC this morning the motif problem is fixed. So I didn't need to use Jerry's reposted patch in the end.