Seems, this is expected behavior by design. Please, look at customer address backend model:
class Mage_Customer_Model_Resource_Address_Attribute_Backend_Street
extends Mage_Eav_Model_Entity_Attribute_Backend_Abstract
{
/**
* Prepare object for save
*
* @param Varien_Object $object
* @return Mage_Customer_Model_Resource_Address_Attribute_Backend_Street
*/
public function beforeSave($object)
{
$street = $object->getStreet(-1);
if ($street) {
$object->implodeStreetAddress();
}
return $this;
}
}
And Mage_Customer_Model_Address_Abstract
/**
* set address street informa
*
* @param unknown_type $street
* @return unknown
*/
public function setStreet($street)
{
if (is_array($street)) {
$street = trim(implode("\n", $street));
}
$this->setData('street', $street);
return $this;
}
/**
* To be used when processing _POST
*/
public function implodeStreetAddress()
{
$this->setStreet($this->getData('street'));
return $this;
}
Since Module ImportExport uses attribute's backend models, so this is expected behavior.