String concatenation work in version 8.2.11 and 8.3.6

hi,all
      for example tableA
      create table tableA (
       id serial,
       a integer,
       b integer,
       c integer
      );
      insert into tableA (a,b,c) values (12,34,56);

then,
      select id from tableA where (a||b||c)=123456;
      in postgresql version 8.2.11,it works.
      but in postgresql version 8.3.6,the error as bellow:
       ERROR:  operator does not exist: integer || integer
       LINE 1: select id from tableA where (a||b||c)=123456;
                                      ^
       HINT:  No operator matches the given name and argument type(s). You might need to add explicit type casts.

is it a bug in 8.2.11 or I install 8.3.6 not completely?