Cannot unmount tape because library slot is already occupied
I have got a strange phenomenon here. I see tape drives going down because the tape cannot be unmounted. This is because the source slot where the active cartridge originally came from has been occupied by another cartridge in the meantime.
I understand that this could happen if you would open the library and put new tapes into random free slots manually but that this should never happen if I use NetBackup to empty the CAP and do a robot inventory.
Could this be an inconsistency in the EMM database?
By the way if I do a robot inventory while the situation described above still persists NetBackup will tell me that the library contents is up to date and that no updates are necessary.
Any hint, no matter how small, is greatly appreciated.