How do we know whether or not we're properly reproducing whatever they're seeing if we don't know what we're seeing?

I've seen scenarios where a set of reproduction steps actually showed two things wrong. QA was sending it back for one of the things, but they didn't say what was wrong, only that something was wrong and here's how to reproduce it. The developer saw the other problem, and fixed it. The result when shipped back to QA?

"You didn't fix the problem, but I opened a new defect now for the other thing you broke."