When migrating to a separate partition, the wubi menu either doesn't get an entry, or gets a partially built entry for the migrated install - whenever a separate /boot partition is used. After booting the first time into the migrated install, and rebooting the Wubi install and running update-grub, the entry is added.
Running a comparison before and after the first boot will likely indicate the problem or debugging Grub (ugh),
When migrating to a separate partition, the wubi menu either doesn't get an entry, or gets a partially built entry for the migrated install - whenever a separate /boot partition is used. After booting the first time into the migrated install, and rebooting the Wubi install and running update-grub, the entry is added. Running a comparison before and after the first boot will likely indicate the problem or debugging Grub (ugh),