Backup Location clean-up

Hi all
I am using Acronis® Recovery for Microsoft Exchange Server® version 1.0 (build 239), on an Exchange 2007 SP2 instance.

Every Saturday night I make a full backup of the Exchange.
In the option of the clean-up job, I specify that I want to delete all backups older than 2 days: in this way I expect that on Tuesday the backup made on the Saturday is deleted.
But this not what happens, it is only deleted after a new full backup is created on the next Saturday.
In the clean-up logs I find no errors

Now is this a "limit" of the software, that it always maintains at least 1 full backup, even if not specified, or I am missing something?

Thank you for your help.