Ylem not passing props into another ylem compoennt

Here is a weird bug:
https://codesandbox.io/s/wwwzqrqr7k

If you un-comment the `mapProps()` bit, which should essentially be a no-op, it starts working as expected.

So... that's kind of weird.

Start with the linked CodeSandbox reproduction and compare the component behavior with mapProps() commented out and enabled. Trace how props are passed between Ylem components; done means the receiving component gets its props without requiring the no-op mapProps() call.

Written by the indexing model from the issue text.