The Dawn theme allows users to add an unlimited number of items to their cart from the product page, even if there is only 1 in stock. The Debut theme used to prevent this and provide an error message.
Only once the user initiates checkout does an error appear stating “Out of stock. Some items are no longer available. Your cart has been updated.” Unfortunately, waiting until a user has already committed to checking is the worst time to notify them of a stock shortage, and it will surely lead to a high number of abandonments. And even if you click “Return to cart”, the quantity doesn’t actually update and remains at the impossible number.
In addition, if the user attempts to increase the impossible quantity from the cart page, it will reset to lowest quantity available with no explanation as to what just happened. Only after trying to increase the quantity a second time does an error display.
This is a UX disaster, so I’m hoping it’s known about and will be fixed soon.