ERROR: failed to add item to the index page

With master (3dbb317d32f4f084ef7badaed8ef36f5c9b85fe6) I'm getting this:
visena=# CREATE INDEX origo_email_part_hdrvl_value_idx ON
public.origo_email_part_headervalue USING btree
(lower(substr((header_value)::text, 0, 1000)) varchar_pattern_ops);
psql: ERROR: failed to add item to the index page
The schema looks like this: create table origo_email_part_headervalue (
entity_idBIGSERIAL PRIMARY KEY, version int8 not null, header_value varchar NOT
NULL, header_id int8 references origo_email_part_header (entity_id), value_index
int NOT NULL DEFAULT0, UNIQUE (header_id, value_index) ); CREATE INDEX
origo_email_part_hdrvl_hdr_id_idxON origo_email_part_headervalue (header_id);
CREATE INDEXorigo_email_part_hdrvl_value_idx ON origo_email_part_headervalue (
lower(substr(header_value, 0, 1000)) varchar_pattern_ops); (haven't tried any
other version so I'm not sure when this started to happen) -- Andreas Joseph
Krogh