bug in edit grid

I have the strange scenario where one of my tables has a primary key with a datatype of varchar, and one record in that
tablehas an empty string key i.e.
 

create table test (   id VARCHAR(255) NOT NULL,   test TEXT,   PRIMARY KEY (id)
) WITHOUT OIDS;

INSERT INTO test (id,test) VALUES ('', 'test string');

In the edit grid when I try to edit the test field the data can't be modified.

I'm using pgadminIII 1.6.3 on WinXP sp2 :)

Cheers
Jeremy