Removing the suggestion that this is a duplicate of bug #846836 as I am now using unity-2d 4.8.0-0ubuntu1 and still see the problem. I have reverted to the standard repository so that I have debug symbols and when I unplug the second screen I see, in dmesg
unity-2d-panel[9053]: segfault at 20b1e57d ip 00582f08 sp bf98209c error 4 in libc-2.13.so[514000+176000]
I will install debug symbols and report the result.
Removing the suggestion that this is a duplicate of bug #846836 as I am now using unity-2d 4.8.0-0ubuntu1 and still see the problem. I have reverted to the standard repository so that I have debug symbols and when I unplug the second screen I see, in dmesg panel[9053] : segfault at 20b1e57d ip 00582f08 sp bf98209c error 4 in libc-2. 13.so[514000+ 176000]
unity-2d-
I will install debug symbols and report the result.