And sure enough, this bug report has the right solution in comment #3 : https://bugs.launchpad.net/ubuntu/+source/debian-installer/+bug/574232/comments/3
"Probably related to Bug #561573 and Bug #551965
Appending partman/alignment=cylinder as kernel boot parameter solved the problem for me."
And sure enough, this bug report has the right solution in comment #3 : /bugs.launchpad .net/ubuntu/ +source/ debian- installer/ +bug/574232/ comments/ 3
https:/
"Probably related to Bug #561573 and Bug #551965
Appending partman/ alignment= cylinder as kernel boot parameter solved the problem for me."