I am using Google Translate so I may not understand your question properly.
You are backing up different resources, files, Exchange, etc. and you would like the backups to use different sets of tapes. However, sometimes your backup takes tapes from the wrong set of tapes.
This happens when a job needs an overwriteable tape and there is no overwriteable tape available in the target media set. Instead of failing your job, it takes an overwriteable tape from another media set. This is by design.
You should make sure that you have sufficient tapes in the targeted media set for your job to complete or change the overwrite protection period of the targeted media set.
You can prevent jobs from taking tapes from other media sets by partitioning your tape library so that each medis set has its own partition. However, note that in this situation, if the job run out of tapes, it will fail.