Singleton annotated class instances are separate for interface and implementation binding

Unless I am doing something wrong, I will expect following binding to get single instance, but I am getting two different instances:

Code (python3):

#!/usr/bin/env python3

import abc
import injector

class SomeInterface(metaclass=abc.ABCMeta):
  """Interface with multiple implementations."""

  @abc.abstractmethod
  def some_method(self) -> None:
    pass


@injector.singleton
class SomeImplementation(SomeInterface):
  """One implementation."""

  def __init__(self):
    print(f'Created instance: {self}')

  def some_method(self) -> None:
    pass

class SomeModule(injector.Module):
  """Injector module."""

  def configure(self, binder: injector.Binder) -> None:
    binder.bind(SomeImplementation)
    binder.bind(SomeInterface, to=SomeImplementation)


def test_singleton() -> None:
  inj = injector.Injector((SomeModule(),), auto_bind=False)

  # Following two create different instances. Expected to be same since the implementation is marked singleton
  print(inj.get(SomeInterface))
  print(inj.get(SomeImplementation))

  # These get the two instances created above.
  print(inj.get(SomeInterface))
  print(inj.get(SomeImplementation))


if __name__ == '__main__':
  test_singleton()

Output:

Created instance: <cli.cli_lib.SomeImplementation object at 0x7f69b1bb3ef0>
<cli.cli_lib.SomeImplementation object at 0x7f69b1bb3ef0>
Created instance: <cli.cli_lib.SomeImplementation object at 0x7f69b1bb3e80>
<cli.cli_lib.SomeImplementation object at 0x7f69b1bb3e80>
<cli.cli_lib.SomeImplementation object at 0x7f69b1bb3ef0>
<cli.cli_lib.SomeImplementation object at 0x7f69b1bb3e80>

Start by reproducing the provided Python example, then trace how bindings for SomeInterface and SomeImplementation are resolved and cached. The issue names no repository files or tests; done means both lookups return the same singleton instance while preserving the interface-to-implementation binding.