Appending data to a tape media

I'm having the followin problem:

Platform:

BE2012 on Server 2003 x64

Servers being backed up are all Win 2003.

When running a full backup job and one tape media is completed filled up, the backup job will stop and ask to insert scratch media, even when there are other tapes almost empty and set to append. Only when I insert a scratch media the job will continue. And it doesn't matter either which "overwrite media option" in the backup exec settings. So I tried both options; "Overwrite scratch media before overwritting recyclable media......." and "Overwrite recyclable media contained in the targeted media set....."

This is bad because I'm wasting a lot of tape drive space = money.

Any help on resolving this issue would be appreciate it.

thanks