Comment 62 for bug 1396379

This was just brought to my attention so I took a look at the source-code. Thanks to oldfred's comment #20 showing part of the installer log that helps isolate the source-code responsible.

It looks like this is a result of this code - written in 2006 - assuming a debconf entry that is empty and in consequence choosing a default device. Adding some debug prints into the code might confirm that and allow it to be fixed.

See specifically line 45 in grubinstaller.py (Python code)

https://git.launchpad.net/ubuntu/+source/ubiquity/tree/ubiquity/components/grubinstaller.py#n45

Calling misc.grub_default() from:

https://git.launchpad.net/ubuntu/+source/ubiquity/tree/ubiquity/misc.py#n370