date whereBetween problem

Hi,

When I try filter records by whereBetween, the filter not works. 

$df= new \DateTime();
$df->modify('-1 month');

$from = Carbon::instance($df);
$now = Carbon::now();
$interactions = Interaction::whereBetween('created_at', array($from, $now))->get();

The problem is that var $interactions is empty.  
