When a spec fails a 'keys*' spec, the 'in' path refers to the path after conforming. This is different from other specs (including 'cat' specs), where the 'in' path indicates the path in the original (pre-conformed) data.

This is confusing for users looking at the default error message, since their original data doesn't have a ':y' key in the example. Furthermore, this makes it difficult for third-party libs to display the bad value in context.