Magento configurable products stock control

This concerns configurable products and associated products in Magento When using inventory we create a master configurable product 1234C then we have associated products 1234C A B C D When ABCD sell out of stock they no longer show up as options for the 1234C however even though there is no stock the main configurable product doesn't go out of stock. (we have it set to not show out of stock products) What we'd like is for it to change the status of the config product to out of stock (so it doesn't show) when all the associated products are sold out. So when we have more assoc back in stock the config shows up again. I don't know why Magento doesn't do this, but we need this done very quickly.