Issue resolving javascript export modules

I am using the latest preact, but it looks like a webpack issue to me.
Let’s say my folder structure is:

• app
  • foo
    • index.js
  • app.js
• bar
  • baz
    • index.js

app/app.js

import { foo } from './foo'
import { baz } from '../bar/baz'
...

app/foo/index.js

const foo = () => { ... }
export { foo }

bar/baz/index.js

const baz = () => { ... }
export { baz }

It fails to bundle with a warning “export ‘baz’ was not found in ../bar/baz

But, if I make it a default export like

bar/baz/index.js

const baz = () => { ... }
export default baz

and update app.js to

app/app.js

import { foo } from './foo'
import baz from '../bar/baz'
...

everything works fine

Just wondering how is it possible that “local” directory reference resolves fine, but level up – can’t be resolved in a list export.