There’s an acknowledged bug in the installer but, due to a complete re-write for forthcoming Electric Eel, there’s believed to be little value in fixing this one. (I submitted this bug and the explanation from iX is along those lines, which I think is fair enough).
The solution which I found to work was to say “yes” to EFI boot and, even though my Gen8 does not EFI boot, the machine starts fine and always has done.
