Commented by: @dyemanov

NBackup is known to have various issues, especially in the older Firebird versions, see CORE2539, CORE1139, CORE2749, CORE2266 for examples. Some of those issues are resolved in the recent v2.1 post-releases, but generally it's recommended to migrate to Firebird 2.5 if you heavily rely on that feature.

Commented by: ABC Mail (abcmail)

Thanks Dimitry, but do you also know how to correct the problem caused by nbackup, leaving the Delta file after backup?

Commented by: Sean Leyne (seanleyne)

The issue has been fixed in case CORE2539/Firebird v2.1.4 as Dmitry noted. There is no workaround to the issue.

Commented by: @dyemanov

Problem with the active delta could be (supposedly) resolved with backup/restore via GBAK.

Commented by: @hvlad

It should be merged automatically after shutdown of all server processes (suppose you used CS)