check contraint allows illegal value?

Is this a bug?

create table foo( c char(2)
    check (c in ('09', '10', '11', '12', 'n/a'))
);
CREATE

insert into foo values('09');
INSERT

insert into foo values('10');
INSERT

insert into foo values('08');
ExecAppend: rejected due to CHECK constraint foo_c

insert into foo values('n/a');
ExecAppend: rejected due to CHECK constraint foo_c



clearly this was a 'whups' on my part, but it would have
been nice to know that my constraint was bogus at the
time the table was created.