Have you worked with Opus 5?
Its documentation about what the code does not do could fill whole books.
UI copy being full of slop explaining what the software does not do is another problem.
I am not convinced that a lack of negative test cases is an issue.
I do agree it generates too much code most of the time.
Documentation is important. I would say Opus' propensity to write documentation that documents non-features is part of the problem being discussed.
And the problem isn't just that it says what the software doesn't do, most of the things it claims are in fact meaningless, it's not even clearly describing something the software shouldn't do.