Case update in API V3 makes case reassign if contact_id is not set

When trying to call Case Close using CiviCRM API V3, something strange happened:

Original Case was Closed (Resolved), but all activities in it deleted
New Case was created as reassign of the original Case - to the same contact, still in status Ongoing.

I have tried to analyze this and found following:

civicrm_api3_generic_update calls Case.get using civicrm api v3 ($existing = civicrm_api($apiRequest['entity'], 'get', $seek)

It then adds the parameters to the request:

$existing = array_pop($existing['values']);
$p = array_merge($existing, $apiRequest['params']);
return civicrm_api($apiRequest['entity'], 'create', $p);

However, in $p is 'contact_id' now not a value, but array:

[contact_id] => Array
(
[1] => 1
)

Then, in _api_case_update is following code:

// check for same contact id for edit Client
if ($params['contact_id'] && !in_array($params['contact_id'], $origContactIds))

{ $mCaseId = CRM_Case_BAO_Case::mergeCases($params['contact_id'], $params['case_id'], $origContactId, NULL, TRUE); }

because $params['contact_id'] is not value, but array, the condition matches (even though actually contact_id and origContstsId[1] have the same value
... and mergeCases is called

I am not sure, in which place is the best to fix this issue. I am posting it here ... and for my personal reasons will implement some temporary fix.

Regards,

Dexter