Today at work I isolated a problem I was having with this function to how I was formatting the date. I was assigning the date in my code as follows:
$today = date( "Ymd" ); // ISO 8601
This format is acceptable to PostgreSQL, as verified by their documentation and buy tests using psql. However, to make it work in my code, I had to make the following change:
$today = date( "Y-m-d" ); // also ISO 8601 format