Backup Exec 12.5 Backup-to-Disk folders won't overwrite

All of my backups are going to Backup-to-Disk folders. I have all the devices and media set to overwrite, but for some reason my hard drive keeps filling up over and over again and I'm having to go in and manually delete backups. Its like the media sets are not overwriting one another. Is this happening because I'm not running Inventory and Catalog jobs? Should these be run after each backup?

I have 3 media sets.. (Exchange1, Exchange2, Exchange3) , then I have 3 backup-to-disk folders (Exchange1, Exchange2, Exchange3), then I have 3 seperate jobs going to each individual backup set and device. Each backup-to-disk folder keeps growing until i'm out of space on the hard drive, not sure why my media sets won't overwrite.

Thanks for the help.