How about this instead?

If true, then in cases where we would have otherwise discarded the stub's return value and returned undefined instead, we go ahead and return it. Specifically, this is any time other than when (a) we are already inside a stub or (b) we are in Node and no callback was provided. Currently we require this flag to be explicitly passed to reduce the likelihood that stub returns values will be confused with server return values; we may improve this in the future.