It took a while to find the right build - it's hidden in the Quantal packages at https://launchpad.net/ubuntu/+source/linux-lts- quantal/3.5.0-23.35~precise1.
I installed the kernel packages, rebooted, and verified that with 3.5.0-23-generic, the issue still occurs in Ubuntu 13.10. This seems to be a userspace issue of some kind. cplummer@cplummer-dl:~$ cat /proc/version Linux version 3.5.0-23-generic (buildd@komainu) (gcc version 4.6.3 (Ubuntu/Linaro 4.6.3-1ubuntu5) ) #35~precise1-Ubuntu SMP Fri Jan 25 17:13:26 UTC 2013 cplummer@cplummer-dl:~$ -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1257327 Title: Ubuntu 13.10 dual monitor screen lock causes windows to disappear off- screen To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1257327/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs