> seems like firebird's rights set up incorrectly? e.g., no write
> permission for a db file?

Ok, at least this is not a "feature" of JayBird. Now you have to answer the
question why other statements work ok :))

> i guess i shall ask fb developers?..

Before asking developers check the owner user and group for the database
file and the access permissions to it. And compare with the user under which
Firebird runs. Note, when you create database with

CREATE DATABASE '/path/to/my/db.fdb' USER 'SYSDBA' PASSWORD 'masterkey';

it is created without talking to your server, but the file is accessed
directly and you're the owner of the file. Same applies to backup/restore
process.

So, if your Firebird runs under firebird user, do simply

chown firebird:firebird /path/to/my/db.fdb

Roman