I don't know if it's a bug, but it can be a problem. After upgrading firbird database, the file /etc/firebird/security.fdb was proposed for change in etc-update. It is a binarie file and the diff in etc-update can't permit to see any significant change. As when I upgrade for X for exemple, I accepted the new binarie file, without knowing exactly what it was. The problem is that this file contains the crypted passwords for database access, and is handled with the /opt/firebird/bin/gsec command. Replacing this file set the database in is default status, with a default password. It seems that this file should'nt be in etc-update because it is not exactly a configuration file. Only the database administrator have to change it, not the system administrator during an update.
The other option is not to move the file, but then it get overritten without further inquiry with the next update.
I don't consider this a bug. It's a core file, granted it's a db and variable. It's storing passwords and the type of stuff that can be found in etc, IMHO. I believe it's best for etc-update to catch that something wants to overwrite that file. So passwords on a server don't just disappear, to be later replaced by a backup if available. Closing bug, thanks for reporting.