insert bug

Hello,

I posted about this to the sql list, but on reflection, it feels a
little bit like a bug.  Either that, or some hole in my understanding of
the way the universe works.  Whatever it is, I wanted to ask the larger
group if there were any opinions on what I am seeing.

I am having strange behavior when I try to do an insert.  Postgres tells
me that it cannot insert a duplicate key into a primary key index, when
I am not trying to insert into it.  Can anyone shed light on why this is
happening, or point out the error of my ways?

Here's a chunk from my query log:
Jul 14 12:48:47 localhost postgres[2998]: [107-1] LOG:  query: INSERT INTO fdata
(fref,fstart,fstop,fbin,ftypeid,fscore,fstrand,fphase,gid,ftarget_start,ftarget_stop)
Jul 14 12:48:47 localhost postgres[2998]: [107-2]
VALUES('XX',7327656,7327658,'1000.007327','41',NULL,'+',NULL,'12358',NULL,NULL)
Jul 14 12:48:47 localhost postgres[2998]: [108] ERROR:  Cannot insert a duplicate key into unique index pk_fdata

and the table definition:
wormbase=> \d fdata
                                      Table "public.fdata"
    Column     |          Type          |                       Modifiers
                                  
---------------+------------------------+--------------------------------------- -----------------
 fid           | integer                | not null default nextval('public.fdata _fid_seq'::text)
 fref          | character varying(100) | not null default ''
 fstart        | integer                | not null default '0'
 fstop         | integer                | not null default '0'
 fbin          | double precision       | not null default '0.000000'
 ftypeid       | integer                | not null default '0'
 fscore        | double precision       |
 fstrand       | character varying(3)   |
 fphase        | character varying(3)   |
 gid           | integer                | not null default '0'
 ftarget_start | integer                |
 ftarget_stop  | integer                |
Indexes: pk_fdata primary key btree (fid),
         fdata_fref_idx btree (fref, fbin, fstart, fstop, ftypeid, gid),
         fdata_ftypeid_idx btree (ftypeid),
         fdata_gid_idx btree (gid)
Check constraints: "chk_fdata_fstrand" ((fstrand = '+'::character varying) OR (f strand = '-'::character varying))
                   "chk_fdata_fphase" (((fphase = '0'::character varying) OR (fp hase = '1'::character varying)) OR
(fphase= '2'::character varying)) 

Note that I do not try to insert anything into fid, the primary key on
this table.  Why does Postgres think I am?

--
------------------------------------------------------------------------
Scott Cain, Ph. D.                                         cain@cshl.org
GMOD Coordinator (http://www.gmod.org/)                     216-392-3087
Cold Spring Harbor Laboratory