When you go through the process of scheduling an Advanced Mass Email, you have the option to have tracking appied, so a Mass Interaction is created for all of those that will receive an email. If you cancel the Advanced Mass Email before it is scheduled to send, the Mass Interaction is are still entered into the Mass Interaction tab of the scheduled recipients of the email.
When you schedule an Advanced Mass Email and choose to create a Mass Interaction for those that are supposed to receive it, the Mass Interaction are immediately created. Even if you cancel the Scheduled Advanced Mass Email, eTapestry does not delete the Mass Interaction.
If you cancel a mass email that uses tracking through Mass Interaction with the intention to reschedule it, you will need to go onto one of the recipients Constituent records and delete the Mass Interaction. Deleting the Mass Interaction on one account will delete it from all the recipient accounts.