A duplication job might write the data to more than one device
A duplication job might write data to not only the specified target device but to a different available device as well.
An environment where Backup Exec has three possible target devices.
These target devices can be Backup to Disk (B2D) folders, Physical libraries or/and Virtual libraries (VTL)
Backup job runs to the specified device #1
Duplication job runs to the specified device #2
This particular issue appears to be happening in some very rare occasions, when the dedicated target device requests a new media because the current media (tape / B2D media) has reached its capacity.
In this situation, after the media request the job continues to duplicate the data to device #3 instead.
This only affects duplication jobs.
This issue is fixed in Hotfix161270 (See Related Articles section)