Comment 15 for bug 683379

grub2/linux_cmdline has been there forever, since well before I was maintaining grub2. I'm not sure whether the grub2 package will be able to sensibly do anything about this - your initial preseeding for these images was wrong if it didn't preseed those.

grub-pc/install_devices_empty has been there for a while, although that code was changed around quite a bit in 1.98-1ubuntu7. Your current preseeding looks fine, but as you say it wasn't there in lucid. I don't know how to correct this without a time machine.