Japan 46 Campaign Supply Sources

[ComradeP]

The Japanese have only 4 corps-sized HQ's, none of which are assigned to any of the armies and only 2 of which are actual HQ organizations that allow attachments. 

Units directly assigned to army HQ's can't be reassigned. That's why such units are sometimes assigned to a "dummy" corps HQ, like in France '40 which also had this issue before the last update.