Currently when using configurable products the stock threshold is not working.
You have a configurable product based on 5 simple products.
Shirt-S (stock 10), Shirt-M (stock 3), Shirt-L (stock 10), Shirt-XL (stock 10) and Shirt-XXL (stock 10).
The stock threshold is set to 5.
When a user clicks size M the stock status should change to: Only 3 in stock.
But it does not.