Why are PROPS carts reset after ajax request in Bitrix?

Question

1C-Bitrix

There is an event that transfers the PROPS values ​​to the basket, the trouble is that if you change the quantity in the basket, then these values ​​\u200b\u200bfly off and put absolutely incomprehensible and where they came from too

AddEventHandler("sale", "OnBeforeBasketAdd", "OnBeforePresentToBasket");
function  OnBeforePresentToBasket(&$arFields)
{
   if(CModule::IncludeModule("iblock"))
   {
       $arFilter = array("IBLOCK_ID" => 17, 'ID' => $arFields['PRODUCT_ID']);
       $arSelect = array('IBLOCK_ID',"ID","PROPERTY_SVOISTVO1","PROPERTY_SVOISTVO1");
       $rsElement = CIBlockElement::GetList(array('SORT' => 'ASC'), $arFilter, false, false, $arSelect);
       if ($arElement = $rsElement->GetNext()) 
       {
           $arFields['PROPS'][] = array(
               'NAME'  => "Свойство 1",
               'CODE'  => "SVOISTVO1",
               'VALUE' => $arElement["PROPERTY_SVOISTVO1_VALUE"],
               'SORT'  => 0
           );
        $arFields['PROPS']['1'] = array(
               'NAME'  => "Свойство 2",
               'CODE'  => "SVOISTVO2",
               'VALUE' => $arElement["PROPERTY_SVOISTVO2_VALUE"],
               'SORT'  => 1
           );
       }
   }
   return;
}