I have the same set up with the same symptoms, however there is a workaround - Bob, when you enable dual monitors log out and back in again and it should be ok, you will need to add a logout button to the panel away from the garbled mess:)
This works but if enabling desktop effects under appearance, the display gets messed up as described above and a log out and back in again somehow reverts it back to "no effects" -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/706890 Title: dual monitors garbled display on 10.10 with Radeon X600 -- ubuntu-bugs mailing list [email protected] https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
