Average age chart not working correctly

[Mark Grimm]

Hello,

I run a report based upon the "Average Age Chart" widget.   Because I look at this chart each month for a period of 60 days, I have an overlap of a month, every month, in the data.  My question is about why the actual counts for past averages change over time. 

For example:

This is a snapshot of the widget taken today.  It shows that the average age of an unresolved issue in September increased and the actual counts approached 65 days average age.

The following is a snapshot taken about the same time, 30 days ago.  In this older image, we can see that the average age for the last two weeks in September hovers around 23 instead of 65 as shown in the current-month's image, above.

There is a significant difference between an average age of 23 days and an average age of 55 or 60.   Shouldn't the data be the same for a given week, regardless of when it's viewed in time?

Please note that no other factors have changed; the query remains the same and reactivations are extremely rare.  

Thank you.

-Mark