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