Some functionality should be common sense to a competent developer, and not have to be specified. As a developer, I'd expect working code to have the following behavior, whether or not it was explicitly written into the spec:

- If the credit card transaction fails, do not ship the product to the customer, and notify the customer of the failure.

- Don't let the customer order more items than are available in our inventory, or zero items, or a negative or non-integer number of items.

- A web-based system should correctly handle multiple concurrent transactions.

- If something goes wrong, show the user a meaningful error message in their selected language, not a Python stack trace.

If my excuse for my code not doing this was "it wasn't in the spec", I'd expect people to ridicule me.

"working as expected" doesn't preclude defects. As expected by whom? There's always a range of expectations to consider... take the iPhone4 antenna, was it a bug or just people "holding it wrong"/ intentionally squeezing the phone to demonstrate signal loss?

Or, take programming languages - is the null pointer "working as expected", or is it a "billion dollar mistake"?

Unfortunately many companies don’t differentiate.