LP:857066 - Wrong result with ST_DISJOINT when using an index

The following query:

SELECT count FROM linestring FORCE KEY ( linestring_key ) WHERE ST_DISJOINT( GeomFromText('LINESTRING( 4045 3043 , 3987 3025 , 3757 3154 )') , linestring_key );

returns 300 rows even though the same query executed with a full table scan or in PostGis returns 3711 rows.