Alter domain success but expression index fail then

[livius2]

CREATE DOMAIN DOMAIN_REGION VARCHAR(5);
CREATE TABLE REGION
(NAME DOMAIN_REGION );

CREATE INDEX IXAE_REGION__NAME ON REGION COMPUTED BY(UPPER(NAME));
commit;

INSERT INTO REGION(NAME) VALUES('12345');
INSERT INTO REGION(NAME) VALUES('abcde');

commit;

ALTER DOMAIN DOMAIN_REGION TYPE VARCHAR(20);

commit;

now try to update table to use extended length of the domain.

UPDATE REGION SET NAME = NAME || '67890';

Message: isc_dsql_execute2 failed

Engine Code    : 335545153
Engine Message :
unknown ISC error 335545153
arithmetic exception, numeric overflow, or string truncation
string right truncation
expected length 5, actual 10

If you drop index IXAE_REGION__NAME, then above update is working.

3 things to improve this:

1. update index too if have dependency of domain. or
2. raise an error about index dependency when altering domain. or
3. improve error message and write there that reason of an error is IXAE_REGION__NAME.

Now it is nightmare to find exect reason what happened, where this truncation occur, especially if db structure is not trivial as above sample ;-)