> I've started using NBackup lock + local file copy + Nbackup unlock
> (merge the delta file) for backing up my FB 2.5 database.
>
> After the copy has been completed, I do Nbackup fixup (remove the lock
> but don't try to merge any delta file) on the local copy and then
> transfer it to a remote backup volume. After that I use the local copy
> for test/development/debug purposes.
>
> I've noticed that after this process, the local copy (now operating as a
> test database) has a stuck OIT, so a sweep is required.
>
> Why does that happen,

It is because in locked database there is always at least one transaction active.

> and is there a quicker way than a full sweep to solve it?

I do not think so.

Ivan