Mixin classes don't allow constructors of _generic_ 'object' types

TypeScript Version: 2.3.4, 2.4.0-dev.20170609

Code:

type Constructor<T> = new (...args: any[]) => T;

const Timestamped = <I extends object, CT extends Constructor<I>>(Base: CT) => {
  return class extends Base {
    timestamp = new Date();
  };
};

Expected behavior:

Should be able to use the generic I as an argument to Constructor.

Actual behavior:

Compiling this yields the following error:

error TS2509: Base constructor return type 'I' is not a class or interface type.

Note:

This is a variation on https://github.com/Microsoft/TypeScript/issues/13805 where the following compiles successfully:

type Constructor<T> = new (...args: any[]) => T;

const Timestamped = <CT extends Constructor<object>>(Base: CT) => {
  return class extends Base {
    timestamp = new Date();
  };
};

Start with the TypeScript compiler's handling of generic constructor return types and reproduce the example from the issue using TypeScript 2.3.4 or the referenced development version. Done means the generic I can be used as the Constructor argument without TS2509, while the object variant and existing mixin behavior continue to compile.