How can the LEFT JOIN return more results than the unjoined query?
Each row in the first table may match more than one row in the second table.

You can check this with:

SELECT l.id,count(*) 
FROM list l 
LEFT JOIN cardinal c ON l.id=c.id 
WHERE c.resolution IN ('Left','Right','Up') AND l.source='blink' 
group by l.id 
having count(*)&gt;1;


A little demo is on SQL Fiddle here.