I can confirm this on my machine as well. The WARNING will be in the terminal window after clicking "Upgrade" in the update-manager. I will talk to someone about marking this "Triaged" right away. Thanks for reporting it.
** Changed in: update-manager (Ubuntu) Status: New => Confirmed -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/742101 Title: update-manager can't handle sources.list containing deb [arch=$arch] style lines -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs