A box job is defined with a box_success attribute that contains only global variable conditions. When the conditions become satisfied, the box does not change to success like it would if the box_success was set to a job condition.
The box_success evaluation does not treat global variable conditions exactly the same as it treats a job condition. The box_success is not triggered immediately when the global variable is set. At least one of the jobs in the box must complete after the variable is set before the box job will go to success.