CTaskItem::update

public function update($arNewTaskData = [], array $parameters = array())
{
	if (empty($arNewTaskData))
	{
		return;
	}

	if (
		!array_key_exists('PIN_IN_STAGE', $parameters) ||
		array_key_exists('PIN_IN_STAGE', $parameters) && $parameters['PIN_IN_STAGE']
	)
	{
		self::pinInStage($this->getId(), $arNewTaskData);
	}

	$this->proceedAction(
		self::ACTION_EDIT,
		array('FIELDS' => $arNewTaskData, 'PARAMETERS' => $parameters)
	);

	// drop gmt cache
	$this->startDatePlanGmt = 	null;
	$this->endDatePlanGmt = 	null;
}