Tape storage shown as Full (32 GB), but saveset only has files with 3.2 GB


We are using NetVault Backup 10.0 to backup files to a distant storage device.

It has 2 drives and 8 slots (As shown in the Manage Devices section), each with 32 GB capacity. 

In one of the slots, if I check the Explore Storage->Explore tape storage->Select the slot label and click "Explore Media", I can see 2 savesets with 2.59GB size (Each), but the details of that slot show entire 32 GB is used.

Can someone explain to me what other data is stored here? and how to clear that data. I have seen this behavior in all slots, and what I used to do is blank the tape, relabel it and assign it to the job again.

Backup Job is set with backup life as "Discard after 2 Backups"