When creating an Element with a ref from inside of a constructor an error is thrown in production mode, but not in dev mode.

Here is a minimal sample:
https://jsfiddle.net/84v837e9/35/

An error, "Only a ReactOwner can have refs", should happen in dev and production modes.

This is happening in React 15.4
ReactDOMStack.unmountComponentAtNode(this._container);
      }
    }
    const container = document.createElement('div');
    const a = ReactDOMFiber.render(<A />, container);
    expect(a.refs.span).toBeTruthy();
    ReactDOMFiber.unmountComponentAtNode(container);
    expect(a.refs.span).toBe(undefined);
    expect(layerMounted).toBe(true);
  });
  it('attaches, detaches from stack component with fiber layer', () => {
    const ReactCurrentOwner = require('ReactCurrentOwner');
    const ReactDOM = require('ReactDOMStackEntry');
    const ReactDOMFiber = require('ReactDOMFiberEntry');
    const ReactInstanceMap = require('ReactInstanceMap');
    let layerMounted = false;
    class A extends React.Component {