On further investigation, this seems to be a bug in the latest intel graphics drivers. Using synaptic, I downgraded the package xserverxorg- video-intel to version 2:2.9.0-1ubuntu2 and the problem went away.
-- Thrown back to login-screen running Ubuntu 9.10 https://bugs.launchpad.net/bugs/502663 You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
