FYI, the problem seems to be that ubiquity is running things in parallel and/or in the wrong order. Specifically, it is running the partman visual.d scripts first, which add the new partitions, and then the init.d scripts after, which detect the newly added partitions and thinks they are existing partitions of an existing bios mode install.
FYI, the problem seems to be that ubiquity is running things in parallel and/or in the wrong order. Specifically, it is running the partman visual.d scripts first, which add the new partitions, and then the init.d scripts after, which detect the newly added partitions and thinks they are existing partitions of an existing bios mode install.