Create a test case that covers #136 and #137

We saw odd serialization behavior in #136 and #137 that we closed with #139 and #142.

We only verified our fixes with manual testing though -- ideally this would be covered by a test case or two.

We should also investigate why the model-level exclude config didn't seem to have the desired outcome (we had to use the `dict(exclude={...}` method)

