In comment #18 you mention that the output is from Lucid before running update-manager and in that comment 'grub-pc/install_devices: ' is empty. This means that some time during Lucid, or when installing the sytem, this choice was made.
In comment #18 you mention that the output is from Lucid before running update-manager and in that comment 'grub-pc/ install_ devices: ' is empty. This means that some time during Lucid, or when installing the sytem, this choice was made.