Incremental & Full backup - Associate media set

Dear Sirs,

We are using BE12 and HP24 tapes . BE is been setup to run full backup ( every Friday at 11pm ) and backup ( every day at 4am ).

The media set of the tapes are associate as shown below:

Incremental backup: tapes 1-18

Full backup: tapes 19-24

The issue we are experiencing is that the full backup is using random tapes from the tapes which are associate with incremental backup. Upon completion of the full backup those tapes change the media set from incremental to full backup.

Please advise how to solve this issue in order full backups to use the tapes 19-24.

Full backup media set:

Incremental backup media set:

Backup job:

Thanks in advance.

Dimitris