No stock_available section for newly created product via Prestashop webservices

as the title says, I can successfully create a new Product via Prestashop 1.6.1 webservice. The problem is that the new product XML has an empty stock_available section:

<stock_availables nodeType="stock_available" api="stock_availables" />

so I have no idea how to set the initial quantity for that product. If I set it manually from the back office, the stock_available section is filled.

Maybe there is something I'm missing in the XML request? Here it is:

<?xml version="1.0" encoding="UTF-8"?>
<prestashop xmlns:xlink="http://ift.tt/PGV9lw">
<product>
    <id/>
    <id_manufacturer/>
    <id_supplier/>
    <id_category_default>52</id_category_default>
    <new/>
    <cache_default_attribute/>
    <id_default_image/>
    <id_default_combination/>
    <id_tax_rules_group/>
    <position_in_category/>
    <type/>
    <id_shop_default/>
    <reference>A130</reference>
    <supplier_reference/>
    <location/>
    <width/>
    <height/>
    <depth/>
    <weight/>
    <quantity_discount/>
    <ean13/>
    <upc/>
    <cache_is_pack/>
    <cache_has_attachments/>
    <is_virtual/>
    <on_sale/>
    <online_only/>
    <ecotax/>
    <minimal_quantity/>
    <price>1.30</price>
    <wholesale_price/>
    <unity/>
    <unit_price_ratio/>
    <additional_shipping_cost/>
    <customizable/>
    <text_fields/>
    <uploadable_files/>
    <active>1</active>
    <redirect_type/>
    <id_product_redirected/>
    <available_for_order>1</available_for_order>
    <available_date/>
    <condition/>
    <show_price>1</show_price>
    <indexed>1</indexed>
    <visibility/>
    <advanced_stock_management/>
    <date_add/>
    <date_upd/>
    <pack_stock_type/>
    <meta_description>
      <language id="1" xlink:href="http://ift.tt/2hiZ0JU"><![CDATA[product name]]></language>
    </meta_description>
    <meta_keywords>
      <language id="1" xlink:href="http://ift.tt/2hiZ0JU"><![CDATA[product name]]></language>
    </meta_keywords>
    <meta_title>
      <language id="1" xlink:href="http://ift.tt/2hiZ0JU"><![CDATA[product name]]></language>
    </meta_title>
    <link_rewrite>
      <language id="1" xlink:href="http://ift.tt/2hiZ0JU"><![CDATA[product name]]></language>
    </link_rewrite>
    <name>
      <language id="1" xlink:href="http://ift.tt/2hiZ0JU"><![CDATA[product name]]></language>
    </name>
    <description>
      <language id="1" xlink:href="http://ift.tt/2hiZ0JU"><![CDATA[product name]]></language>
    </description>
    <description_short>
      <language id="1" xlink:href="http://ift.tt/2hiZ0JU"><![CDATA[product name]]></language>
    </description_short>
    <available_now>
      <language id="1" xlink:href="http://ift.tt/2hiZ0JU"><![CDATA[product name]]></language>
    </available_now>
    <available_later>
      <language id="1" xlink:href="http://ift.tt/2hiZ0JU"><![CDATA[available later]]></language>
    </available_later>
<associations>
<categories>
    <category>
    <id/>
    </category>
<category>
      <id>52</id>
    </category>
      </categories>
<images>
    <image>
    <id/>
    </image>
</images>
<combinations>
    <combination>
    <id/>
    </combination>
</combinations>
<product_option_values>
    <product_option_value>
    <id/>
    </product_option_value>
</product_option_values>
<product_features>
    <product_feature>
    <id/>
    <id_feature_value/>
    </product_feature>
</product_features>
<tags>
    <tag>
    <id/>
    </tag>
</tags>
<stock_availables>
    <stock_available>
    <id/>
    <id_product_attribute/>
    </stock_available>
</stock_availables>
<accessories>
    <product>
    <id/>
    </product>
</accessories>
<product_bundle>
    <product>
    <id/>
    <quantity/>
    </product>
</product_bundle>
</associations>
</product>
</prestashop>

Thank you for any help!

Iuri