Augmenting external module that is re-exported?

TypeScript Version: 2.5.2

Code

This can't be demonstrated with a simple 1-file code example so I made a trivial project to demo it:
https://github.com/chriseppstein/typescript_module_augmentation_bug

Instructions for how to run the demo and work around the issue are included on the README there.

When I include an interface in a node module's main index.ts file, then it is open for merging with a declare module "my_npm_module" {} but when I move that interface into a local submodule and export it in the main index.ts with a export * from "./local_module"; then the downstream consumer breaks.

Expected behavior:

It seems to me that the point of being able to export from other modules is to keep downstream consumers protected from internal refactors and maintain an existing public API. So I expect to be able to augment an interface and have it behave the same whether or not it has been re-exported.

Actual behavior:

It looks like the interface gets forked into two definitions, the downstream module sees only the interface surface that was added and the upstream module only sees the interface surface it defined.

Start with the linked typescript_module_augmentation_bug repository and follow its README instructions to reproduce the issue. Compare augmentation behavior when the interface is declared in index.ts with behavior when it is re-exported from a local submodule. Done means the upstream and downstream modules see one consistent augmented interface.