Difference in `Layer.mock` Behavior with `Context.Tag` vs `Effect.Service`

class MyService extends Context.Tag('MyService')<MyService, { fn(): Effect.Effect<number> }>() {}
Layer.mock(MyService, { fn: () => Effect.succeed(2) })

class MyService2 extends Effect.Service<MyService2>()('MyService2', {
    succeed: { fn: () => Effect.succeed(2) },
}) {}
Layer.mock(MyService2, { fn: () => Effect.succeed(2) })
//                     ^ Property `_tag` is missing.

Layer.mock(MyService2, { _tag: MyService2.key, fn: () => Effect.succeed(2) })