A user sends a mass email to a group.
That user then goes into one of the person records that have received this email.
They then view this under the communication tab and delete the email.

The user then navigates to another person record that received the email but the email is not under the communication tab.

If one of the communications on one of the recipients in the group is deleted all the emails for othe people in that group are deleted.

More information:

This issue is currently with development and will be resolved in a future release of Sage CRM.