Shouldn't FB2 delete master records after detail records if an 'on
delete cascade' clause is used (otherwise the referential integrity
would be violated)?

An example to illustrate the point:

CREATE EXCEPTION EX_ERROR 'Master record should be deleted after
detail record';

CREATE TABLE T1(
U1 BIGINT PRIMARY KEY);

CREATE TABLE T2(
U2 BIGINT PRIMARY KEY,
U3 BIGINT REFERENCES T1(U1) ON DELETE CASCADE);

SET TERM ^;

CREATE TRIGGER TR2 FOR T2
ACTIVE BEFORE DELETE POSITION 0 AS
BEGIN
IF (NOT EXISTS(SELECT U1 FROM T1 WHERE T1.U1=1)) THEN
EXCEPTION EX_ERROR;
END^

SET TERM ;^

COMMIT;

INSERT INTO T1 VALUES(1);

INSERT INTO T2 VALUES(1,1);

DELETE FROM T1;

COMMIT;

The exception is triggered! Any ideas?