activity get API changed (broken in 4.4.x upgrade?), no longer able to limit request to one contact id

somewhere along the way between 4.3.x and 4.5.x the api changed and it is no longer possible to get activities of a specific type that are connected to a specific cid

here is the code I have in place that worked until I did an upgrade to 4.5.x

// looks to see if activity already exists

$params_activity_check = array(
'version' => 3,
'sequential' => 1,
'activity_type_id' => 50,
'activity_date_time' => $visit_date,
'source_contact_id' => $school_cid,
);
$result_activity_check = civicrm_api('activity', 'get', $params_activity_check);

if ($result_activity_check['count'] ==0) {
// create the activity

it now brings back an array of every activity of that type, no matter what cid is associated.
this means that my code now needs to loop over the array which grows by thousands of activities each semester to find if the one I'm looking for exists. that seems very inefficient

the source_contact_id is still in the array returned, but can no longer be used in the get request. I hope this is a bug and not an intentional change.

based on the following unanswered issues in the forum, it seems I'm not the only one with this problem

http://forum.civicrm.org/index.php/topic,21685.msg90883.html#msg90883

http://forum.civicrm.org/index.php/topic,5548.msg24388.html#msg24388

http://forum.civicrm.org/index.php/topic,31672.msg135725.html#msg135725