芹菜节拍每分钟运行一次，而不是每15分钟一次

Question

我正在设置芹菜的时间表

CELERYBEAT_SCHEDULE = {
    'update_some_info': {
        'task': 'myapp.somepath.update_some_info',
        'schedule': crontab(minute='*/15'),
    },
}

检查crontab中实际写的内容时，的确是<crontab: */15 * * * * (m/h/d/dM/MY)>

但是我的芹菜记录表明任务每分钟都在运行

INFO 2020-01-06 13:21:00,004 beat 29534 139876219189056 Scheduler: Sending due task update_some_info (myapp.somepath.update_some_info)
INFO 2020-01-06 13:22:00,003 beat 29534 139876219189056 Scheduler: Sending due task update_some_info (myapp.somepath.update_some_info)
INFO 2020-01-06 13:23:00,004 beat 29534 139876219189056 Scheduler: Sending due task update_some_info (myapp.somepath.update_some_info)
INFO 2020-01-06 13:24:28,255 beat 29534 139876219189056 Scheduler: Sending due task update_some_info (myapp.somepath.update_some_info)

为什么芹菜不击败我的日程安排？