apollo-client: Interface query with conditional fragments breaks after v0.8.7

Intended outcome:

I have a query like this in my app:

  fragment ItemIndexFragment on Item {
    id
    name

    ... on SpecialItem {
      field1
      field2
    }
    ... on ExtraSpecialItem {
      field3
      field4
    }
  }

Expected outcome is that this query just works with a watchQuery.

Actual outcome:

While upgrading ember-apollo-client to the latest apollo-client (and my app that uses it), I encountered a specific route that broke during the upgrade. The watchQuery observable’s next function gets called with data: undefined and stale: true. AFAICT, the only thing special about this route is the fact that it is on an Interface type and includes conditional fragments depending on the result type.

If I remove the conditional fragments, the query “works”, except without the data I want.

I was upgrading all the way from v0.6.0. Bisecting with apollo-client versions revealed that the query worked as expected all the way through v0.8.7. At v0.9.0, I encountered https://github.com/apollographql/apollo-client/issues/1336, and with v0.10.1, I experience the described broken behavior.

How to reproduce the issue:

Issue a watchQuery on a Interface type with a query that includes conditional fragments on the result type.

Unsure if this is related to #1337 but it’s the only thing I could find that seemed like it might be.

Edit: d’oh, updated to reflect that this was a query on an Interface type, not a Union