Move Item in backpack seems working in a wrong way

when i move item in backpack via shift + leftclick, it just combine the stacks in backpack like this gif.It should have transfered the items to inventory i think.

the dest in Invslot:TradeItem got the correct result(inventory) ,but inventory:GiveItem seems will check the retained items in inv and overflow then combine the stack first when the slot_number is not specified.

function InvSlot:TradeItem(stack_mod)
	...
  if not dest:GiveItem(item, nil, nil, nil, true) then --dest is inventory at this time
    container:GiveItem(item, slot_number, nil, true)
  end
  return
end

function Inventory:GiveItem( inst, slot, screen_src_pos, skipsound,dontDropOnFail )
  ...
     if slot then
        local olditem = self:GetItemInSlot(slot)
        can_use_suggested_slot = slot ~= nil and slot <= self.maxslots and ( olditem == nil or (olditem and olditem.components.stackable and olditem.prefab == inst.prefab)) and self:CanTakeItemInSlot(inst,slot)
    end

    local container = self.itemslots
    if not can_use_suggested_slot then --can_use_suggested_slot == false at this time, if no same prefab in inventory
		slot,container = self:GetNextAvailableSlot(inst) -- container is the backpack's and slot_num belongs to backpack's container
    end
  ...
end