BUG #2974: broken CHECK constraint with varchar

The following bug has been logged online:

Bug reference:      2974
Logged by:          Michal Schwarz
Email address:      misch@czechin.cz
PostgreSQL version: 8.1.7
Operating system:   Fedora Core 6
Description:        broken CHECK constraint with varchar
Details:

CREATE TABLE t (c VARCHAR(20));
ALTER TABLE t ADD CONSTRAINT xyz CHECK (c IN ('A','B','C'));
INSERT INTO t VALUES ('A');

Results:
ERROR:  attribute 1 has wrong type
DETAIL:  Table has type character varying, but query expects character
varying.

In previous versions, everything worked correctly. Problem arised in 8.1.7
(maybe only in Fedora release???). When i returned back to 8.1.6, everything
worked again.