confounding, incorrect constraint error

I've hit some really evil nastiness that is either a Postgres 7.1.3 bug,
or signs of early-onset senility for me.  I was having trouble with my
database dying while inserting some values, and running some PL/pgSQL.

The schema is as listed below, and I'm getting 
psql:fuck.sql:175: ERROR:  ExecReplace: rejected due to CHECK constraint users_logged_in
while inserting values into the uservote table.  If I had a few columns to
the users table, postgres crashes instead of giving this (nonsensical)
error.

I'd greatly appreciate any insight, even if it involves a 2x4.

Below is a significantly simplified version of my schema, which exhibits
the above problem.

DROP RULE uservote_update_item_mod;
DROP RULE uservote_delete_item_dec;
DROP RULE uservote_insert_item_inc;

DROP RULE itemvote_update_item_mod;
DROP RULE itemvote_delete_item_dec;
DROP RULE itemvote_insert_item_inc;

DROP FUNCTION mod_node_vote_count(INT4, INT2, INT2);

DROP TABLE uservote;
DROP TABLE itemvote;

DROP TABLE item;
DROP TABLE users;
DROP TABLE node;

DROP SEQUENCE node_id_seq;

CREATE SEQUENCE node_id_seq;

CREATE TABLE node (       node_id         INT4 UNIQUE NOT NULL DEFAULT nextval('node_id_seq'),       name
TEXTNOT NULL,       nays           INT4 NOT NULL DEFAULT 0                           CHECK ( nays >= 0 ),       yays
      INT4 NOT NULL DEFAULT 0,                           CHECK ( yays >= 0 ),       rating          INT2 NOT NULL
DEFAULT50                           CHECK ( rating >= 0 AND rating <= 100 ),       PRIMARY KEY (node_id)
 
);       
CREATE TABLE users (       node_id         INT4 UNIQUE NOT NULL,email           TEXT NOT NULL,realname    TEXT NOT
NULL,pass_hash   VARCHAR(32) NOT NULL,       logged_in    INT2 NOT NULL DEFAULT 0                            CHECK
(logged_in= 0 OR logged_in = 1)
 
) INHERITS (node);

CREATE TABLE item (       node_id         INT4 UNIQUE NOT NULL,creator_id    INT4 NOT NULL
REFERENCESusers (node_id)                           ON DELETE CASCADE                           ON UPDATE CASCADE,
reason       TEXT NOT NULL
 
) INHERITS (node);    

CREATE TABLE itemvote (vote_date    TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,target_id       INT4 NOT NULL
                REFERENCES item (node_id)                            ON DELETE CASCADE                           ON
UPDATECASCADE,       user_id         INT4 NOT NULL            REFERENCES users (node_id)            ON DELETE CASCADE
             ON UPDATE CASCADE,nays        INT2 NOT NULL                           CHECK (nays = 0 OR nays = 1),
 
PRIMARY KEY (user_id, target_id)
);

CREATE TABLE uservote (vote_date    TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,target_id       INT4 NOT NULL
                REFERENCES users (node_id)                            ON DELETE CASCADE                           ON
UPDATECASCADE,       user_id         INT4 NOT NULL            REFERENCES users (node_id)            ON DELETE CASCADE
             ON UPDATE CASCADE,nays        INT2 NOT NULL                           CHECK (nays = 0 OR nays = 1),
 
PRIMARY KEY (user_id, target_id)
);

-- modifies an items nays/yays count totals as appropriate
-- first arg: item number
-- second arg: 1 or 0, nays or yays.
-- third arg: 1 or 0, add a vote, or remove a vote
CREATE FUNCTION mod_node_vote_count (INT4, INT2, INT2) RETURNS INT2 AS '   DECLARE       node_num ALIAS for $1;
nay_statusALIAS for $2;       add ALIAS for $3;
 
       nay_tot INT4 NOT NULL DEFAULT 0;       yay_tot INT4 NOT NULL DEFAULT 0;   BEGIN       IF add = 1       THEN
    IF nay_status = 1           THEN               UPDATE node SET nays = nays + 1 WHERE node_id = node_num;
ELSE              UPDATE node SET yays = yays + 1 WHERE node_id = node_num;           END IF;       ELSE           IF
nay_status= 1           THEN               UPDATE node SET nays = nays - 1 WHERE node_id = node_num;           ELSE
         UPDATE node SET yays = yays - 1 WHERE node_id = node_num;           END IF;       END IF;       SELECT nays
INTOnay_tot FROM node WHERE node_id = node_num;       SELECT yays INTO yay_tot FROM node WHERE node_id = node_num;
 
       IF nay_tot + yay_tot != 0       THEN           UPDATE node SET rating = CEIL( (yay_tot * 100)/(yay_tot +
nay_tot)) WHERE node_id = node_num;       ELSE           UPDATE node SET rating = 50 WHERE node_id = node_num;
ENDIF;
 
       RETURN 1;   END;
' LANGUAGE 'plpgsql';

------------------------------------------------------------------------
-- vote totalling rules

-- vote insertion
CREATE RULE itemvote_insert_item_inc AS   ON INSERT TO itemvote DO       SELECT mod_node_vote_count(NEW.target_id,
NEW.nays,1);
 

CREATE RULE uservote_insert_item_inc AS   ON INSERT TO uservote DO       SELECT mod_node_vote_count(NEW.target_id,
NEW.nays,1);
 

-- vote deletion
CREATE RULE itemvote_delete_item_dec AS   ON DELETE TO itemvote DO       SELECT mod_node_vote_count(OLD.target_id,
OLD.nays,0);
 

CREATE RULE uservote_delete_item_dec AS   ON DELETE TO uservote DO       SELECT mod_node_vote_count(OLD.target_id,
OLD.nays,0);
 

-- vote updates
CREATE RULE itemvote_update_item_mod AS   ON UPDATE TO itemvote WHERE OLD.nays != NEW.nays DO       (SELECT
mod_node_vote_count(OLD.target_id,OLD.nays, 1);        SELECT mod_node_vote_count(NEW.target_id, NEW.nays, 0););
 

CREATE RULE uservote_update_item_mod AS   ON UPDATE TO uservote WHERE OLD.nays != NEW.nays DO       (SELECT
mod_node_vote_count(OLD.target_id,OLD.nays, 1);        SELECT mod_node_vote_count(NEW.target_id, NEW.nays, 0););
 

-- users
INSERT INTO users (name, pass_hash, realname, email) VALUES ('mosch', 'dafe001b7733b0f3236aa95e00f8ed88', 'Kevin',
'monica@whitehouse.gov');
INSERT INTO users (name,  pass_hash, realname, email) VALUES ('Wakko', 'c6ef90fcf92bf703c3cc79a679c192a3', 'Alex',
'wakko@bitey.net');

-- items
INSERT INTO item (name, creator_id, reason) VALUES ('slashdot.org', 2, 'Because it\'s a pile of turd.');
INSERT INTO item (name, creator_id, reason) VALUES ('Yahoo!', 2, 'Because it\'s ugly.');
INSERT INTO item (name, creator_id, reason) VALUES ('memepool', 1, 'Because it\'s phat phat phat phat phat.');
INSERT INTO item (name, creator_id, reason) VALUES ('blow!!??!!', 1, 'this record nays nays nays');

-- item votes
INSERT INTO itemvote (target_id, user_id, nays) VALUES (3, 1, 1);
INSERT INTO itemvote (target_id, user_id, nays) VALUES (4, 1, 0);
INSERT INTO itemvote (target_id, user_id, nays) VALUES (5, 2, 1);

-- user votes
INSERT INTO uservote (target_id, user_id, nays) VALUES (2, 1, 0);
INSERT INTO uservote (target_id, user_id, nays) VALUES (1, 2, 1);