TypeScript: DeepPartial breaks when using unknown

[OliverJAsh]

Repro:

type State = {
  bar: unknown;
};

declare let preloadedState: State;

declare const reducer: Reducer<State>;
createStore(
  reducer,
  // Unexpected type error:
  /* Argument of type 'State' is not assignable to parameter of type 'DeepPartial<State>'.
  Types of property 'bar' are incompatible.
    Type 'unknown' is not assignable to type 'DeepPartial<unknown> | undefined'.
      Type 'unknown' is not assignable to type 'DeepPartial<unknown>'. */
  preloadedState,
);

type StateDP = DeepPartial<State>;
declare let stateDP: StateDP;
// Unexpected type error:
// Type 'State' is not assignable to type 'DeepPartial<State>'
stateDP = preloadedState;