After several reboots the problem seems to be fixed. sorry for inconvenients. But alt +tab in crashing windows manager
-- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/687445 Title: The strange white lines appeared on the top of screen -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs