Blueprint Child set to defults BUG!

I created blueprint from the class Actor (BP_Base_Item_Place_Holder) then I created an child class from it blueprint (BP_inventory_main_child). In a parental class (BP_Base_Item_Place_Holder) i create variable Class.Actor (InventoryClass) and set this variable defult value - BP_inventory_main_child. And my script work well !! BUT when i reload my UE4 editor. In my BP_Base_Item_Place_Holder variable (InventoryClass) is NONE ! How fix this BUG??

windows 7, version 4.6.1