Strange delete behaviour

Hello,

I have a strange delete behaviour in my postgres 8.0.3 database:

If I try a

delete
     from   t_node
     where  node_doc_id = XX;

from inside a plpgsql function

on this table:

CREATE TABLE  t_node  (
    node_global_id     int4 DEFAULT nextval('seq_node')  NOT NULL ,
    node_doc_id        int4 NOT NULL ,
    node_local_id      int4 NOT NULL ,
    node_offset        int4 NOT NULL ,
   FOREIGN KEY ( node_doc_id )
      REFERENCES  t_document ( doc_id )
      MATCH FULL ,
   PRIMARY KEY ( node_global_id )
);

CREATE UNIQUE INDEX idx_node ON t_node (
    node_doc_id
    node_local_id
);

The deletion does not finish after several minutes and the CPU is
running at 100% all the time unless I stop postmaster. A select works
normal and gives me around 2500 rows. Does anybody has an idea why this
happens?

Thanks,
renzo