[Federation] Identical Interfaces not allowed

I'm using the latest verion of apollo server and apollo gateway. I've implemented two federated endpoints (in PHP) here:
* https://tatooine-dev-graphql.wmflabs.org/graphql/federation
* https://jakku-dev-graphql.wmflabs.org/graphql/federation

Both of these endpoints use the same code base, but different databases. I've ensured that all of the interfaces are identical, and the objects are namespaced. For instance `MediaWikiRevision` is an interface of a revision that is identical. There is a `TatooineRevision` and a `JakkuRevision` that both implement the identical interface. I've also ensured that the fields on the interface **only** return other interfaces (not objects).

However, when I try to use these in Apollo Gateway I get the following error:
> GraphQLSchemaValidationError: Field "MediaWikiRevision.revid" can only be defined once.
> Field "MediaWikiRevision.parent" can only be defined once.
> Field "MediaWikiRevision.user" can only be defined once.
> Field "MediaWikiRevision.anon" can only be defined once.
> Field "MediaWikiRevision.timestamp" can only be defined once.
> Field "MediaWikiRevision.size" can only be defined once.
> Field "MediaWikiRevision.sha1" can only be defined once.
> Field "MediaWikiRevision.comment" can only be defined once.
> Field "MediaWikiRevision.parsedcomment" can only be defined once.
> Field "MediaWikiRevision.tags" can only be defined once.
> Field "MediaWikiRevision.roles" can only be defined once.
> Field "MediaWikiRevision.slot" can only be defined once.
> Field "MediaWikiRevision.slots" can only be defined once.
> There can be only one type named "MediaWikiRevision".

According to the [docs](https://www.apollographql.com/docs/apollo-server/federation/core-concepts/#value-types) it's totally accaptable to have overlapping types, as long as they are identical. Doing a [google search](https://www.google.com/search?q=Field+can+only+be+defined+once+apollo+federation) for the error reveals this [unanswered stack overflow question](https://stackoverflow.com/q/56861339/864374).

I'm not sure what the problem is, but according to the documentation, this error shouldn't be thrown... am I missing something?

Start by reproducing schema composition with the two linked federation endpoints and compare the generated interface definitions. Trace the gateway's schema validation for duplicate interface fields; done means identical federated interfaces compose without the reported duplicate-field and duplicate-type errors.

Written by the indexing model from the issue text.