How duplicate data produce when a UNIQUE index exite ?

Dear all,

I have a table as below:

Table "public.t_sfh_history"

Column | Type | Modifiers

-------------+-----------------------------+-----------

idno | character(10) | not null

lo_date | character(8) | not null

line | character(1) | not null

tp | character(2) | not null

bcno | character(3) | not null

times | character(1) | not null

pdate | timestamp without time zone | not null

cdate | timestamp without time zone | not null

psh | character(1) | not null

hdlytime | numeric(6,0) | not null

hspr_tp | numeric(6,0) | not null

hspr_byo | numeric(6,0) | not null

hspr_deli | numeric(6,0) | not null

ltresult | numeric(6,0) | not null

ltresult_bs | numeric(6,0) | not null

dummy | character(6) | not null

Indexes:

"i_sfh_history0" UNIQUE, btree (idno, lo_date, line, tp, times)

When “reindex” operation do,this error occurred:

Nov 22 10:22:27 SUC11 postgres[14145]: [2-1] ERROR: could not create unique index

Nov 22 10:22:27 SUC11 postgres[14145]: [2-2] DETAIL: Table contains duplicated values.

Nov 22 10:22:27 SUC11 postgres[14145]: [2-3] STATEMENT: REINDEX TABLE "t_sfh_history"

My question is:

How the Duplicate datas produce when a UNIQUE index exite ?

Is this a bug of PostgreSQL ?

My postgreSQL version is :

version

----------------------------------------------------------------------------------------------------------

PostgreSQL 8.1.4 on i686-pc-linux-gnu, compiled by GCC gcc (GCC) 3.2.3 20030502 (Red Hat Linux 3.2.3-56)

(1 row)

Thank you very much

Best regards,

Ray Huang