isochrones giving back invalid geometries

[andy-esch]

I used this query:

SELECT 
        CASE WHEN total_pop_area_2011_2015 > 5000
             THEN (cdb_isochrone(the_geom, 'walk', Array[600])).the_geom
             ELSE (cdb_isochrone(the_geom, 'car', Array[600])).the_geom
             END as the_geom,
        address, status, allhomes_zhvi_predenom_2016_08, closed_date, name, state_abb, distance, total_pop_area_2011_2015, male_30_to_34_predenominated_2011_2015, state, phone
FROM
        jc_penny_stores

from this table produces invalid geometries (I created a new table from that query):

This was a problem when I then augmented these polygons with Data Observatory.