We have a set of simple products that are visible in two separate configurable products.
I have set the Maximum Qty Allowed in Shopping Cart to 1, so customers should only be able to order one of each SKU. But it appears they can order two, one from each configurable.
Is there a way to stop this so the customer can only order one simple product, regardless of how many configurables it sits under?
You can use this observer "checkout_cart_product_add_after" to check that the sku may not be same for the product added to cart. Check the condition that in cart is there the same item/sku available then it should not be save in cart. That's it.
Hope it will work for you!.