Problem

The description is misleading:

Project Deadline: Auto-Close Deadline Configuration
This setting is only for API-created Jobs (special flag "calculateDeadlineDate" sent) and overwrites any user assignment defaults. It determines the percentage by which the users jobs will be closed before the project-deadline (if one is set). 100% means, the job deadline equals the project-deadline. Do not set to 0, which would immediately finish the job after creation.
Überschreibbar auf Ebene: Kunde

Solution

Change to:

Job Deadline: Calculate from task deadline
This setting is only for API-created Jobs (special flag "calculateDeadlineDate" sent) and overwrites any user assignment defaults. It determines the percentage by which the user jobs deadlines will be set before the task-deadline (if one is set). 100% means, the job deadline equals the task-deadline. Do not set to 0, which would immediately set the job deadline to the date of creation.
Überschreibbar auf Ebene: Kunde