I noticed this effect when watching the progress of some short (10 minutes)
backup using Data Protector 6.0:

A remote client (Linux) was to be backed up to some file device locally
configured on the HP-UX 11.11 cell server. A media was loaded, and backing up
objects began. After the last object completed, I was expecting Data Protector
to unload the media (and finish the session). However it took minutes until
something happened!
AFAIK the database of Data Protector is updated _after_ the media to write has
been unloaded successfully, so updating the database most likely would not
explain the delay. (Anyway the database is located on an EVA 4000, so it
shouldn't be extremely terribly slow).