find sudstring on text (data type) field failure

I was trying to find a substring on a text (data type) column like 'cat foo
dog ...'.
I use the query below
SELECT id FROM table WHERE name LIKE '% foo %';
Sometimes the query return with nTuples=0 but there are matching rows.
On retry, the query return with expected results. Any ideas;

(postgres ver 9.2, libpq - C Library)