[postgis-users] LWGEOM_gist_joinsel called with incorrect join type

[Ben Madin]

G'day all,

In chasing a list of administrative areas, and the number of reports of disease from within each of them (based on point coordinates) I am using a left outer join from the admin polygon table to the outbreaks table, and st_covers

SELECT n.ccode, n.admin1, count(a5.id) AS "2009" 
FROM new_prov n 
LEFT OUTER JOIN ahis a5 
ON st_covers(n.the_geom, a5.the_geom) 
AND a5.startdate >='2009-01-01' 
AND a5.startdate <  '2010-01-01' 
GROUP BY n.ccode, n.admin1 
ORDER BY ccode, admin1;

are there any problems with getting this notice: 

NOTICE:  LWGEOM_gist_joinsel called with incorrect join type

From trial and error I find that just an (inner) JOIN doesn't give me the notice, but neither do I get a complete list of provinces.

Can I ignore the notice and be confident that I am getting the data I anticipate. Why is this a notice?

cheers

Ben