Order of Activities displayed in CRM 2016 Social Pane.

Hi All,

We are working with CRM 2016 online organization.
There is a social pane(Notes/Activities/Post grid) in case form. We have noticed that order of activities displayed in this social pane are sorted based on modified on descending order.

However some times when we open any completed email or click on  reply/forward, modified on for the original email is changing, there by bringing this email to the top.

Please let us know is this the expected behavior of email and how to customize the order of activities in social pane.

Thanks,
Deepthi