Submitted by: @pcisar

Character fields with UNICODE_FSS charset allow to enter 3x more characters than specified column length.

Test case:

create table T (C1 varchar(10) character set UNICODE_FSS);
commit;
-- All these commands will pass without error
insert into T (C1) values ('1234567890');
insert into T (C1) values ('12345678901234567890');
insert into T (C1) values ('123456789012345678901234567890');
commit;
-- Data are there
select * from T;
-- But Next insert will fail as expected
insert into T (C1) values ('1234567890123456789012345678901');

Note that many (GUI) tools will fail with transliteration/data truncation error on attempt to read the "more than expected" data rows, but ISQL will show these rows.