What backup type do you have setup?
Overwrite Backup
Saves as "_backups\sourcename\data". Does a complete backup every time, if a file is on the destination that is not on the source, it will not be deleted.
Overwrite Backup (Complete/Differential):
Saves as "_backups\sourcename\data". Does a complete backup every time, if a file is on the destination that is not on the source, it will be deleted.
Overwrite Backup (Append):
Saves as "_backups\sourcename\data". Does a complete backup the first time, subsequent backups only send the changes. If a file is on the destination that is not on the source, it will not be deleted.
Overwrite Backup (Differential):
Saves as "_backups\sourcename\data". Does a complete backup the first time, subsequent backups only send the changes. If a file is on the destination that is not on the source, it will be deleted.