demonstration of behavior discussed in http://stackoverflow.com/questions/22389882

1. setup.sql

CREATE TABLE things (
    id integer NOT NULL,
    my_column varchar
);

insert into things (id) values (1);
insert into things (id) values (2);

2. reproduce bug.sql

-- This can be achieved simply with 2 terminal windows each with
-- a psql session

-- Connection A
BEGIN;
UPDATE "things" SET "my_column" = 'hello' WHERE "things"."id" = 1;

-- Connection B
BEGIN;
UPDATE "things" SET "my_column" = 'hello' WHERE "things"."id" = 2;
UPDATE "things" SET "my_column" = 'hello' WHERE "things"."id" = 1;

-- Connection A
UPDATE "things" SET "my_column" = 'hello' WHERE "things"."id" = 2;