Unreliable results returned with PostgreSQL Spatial query?

PostgreSQL version: 9.3.4
PostGIS version 2.1.1
Operating system:  Linux 6.4
Description:

Does the ST_Intersects function have problems returning the correct results=
 with non-box type geometries, like a circle polygon or other style polygon=
s.

i.e.

select count(*) from doti_sensors_report where ST_INTERSECTS(sensor_locatio=
n, ST_Buffer(ST_MakePoint(21.304116745663165, 38.68607570952619)::geography=
, 4000));

thanks