Thought I'd better report a long standing bug thats been around for pretty much the whole life of BE v15 (or at least as long as I can remember). Did a big search first and can't find another post on it but am pretty sure its not just me as I see it at all my sites which use BE v15.
Once jobs complete you cant be assured that the backup sets created as part of the job will actually appear and can be viewed in the storage->media-backup sets view. In extreme cases the backup media will appear to be blank, telling you there are 'no backup sets' when in actual fact, the media might well be full.
The only way I've found to get a view of whats really on the media is to shcedule an inventory window after all backups are done each day. Once the inventory is completed against media it then correctly shows you whats on it.
[edit: I didn't make it very clear above, but this problem also appears to affect tapes, not only disk media. I just did a three tape LTO2 backup. 1 backup set shown on tape #1, none on tape #2 and 1 on tape #3. After inventory and catalog the first tape shows 2 sets, 2nd now shows 1 and third tape shows 2.]
This seems very similar, if not the same issue, of a problem that I have been running into for a while as well.
Try going to the backup sets view for the job itself and not from the storage tab. I beleive you will be able to see the sets from that view without having to run an inventory job.
Will look into this further for possible bug fix.