Minutes listened in a week

When i listened to a big amount of minutes in a week, the minutes of the first day drop of the minutes of the last day get higher. That's when I clicked a week, if I choose 7 days in the calendar it works normally and shows every minute I listened. For example I listened 860 something minutes 7 days ago, but in the weekly thing it shows that I listened 657 and the more minutes I listen today the more the minutes of 7 days ago shrinks. I go to the calender again and it shows the normal.

I don't know if you noticed this, but it took me a time to notice it to.