Comment 3 for bug 30967

I saw something similar when installing Ubuntu on an external USB disk (which by the way works great). I followed the instructions on http://www.ubuntuforums.org/showthread.php?t=80811, which also mentions the problem.

Regularly, after an upgrade, it'd jump back to the wrong settings. I hadn't changed it back yet since last time this happened (hitting 'e' in grub is convenient ;)), but today I found the GRUB record was changed and it now works fine again.

I guess something was changed in the GRUB update scritps. Perhaps this change also fixed this bug for you?