Google Closure Compiler complaining about XMLHttpRequest.response type

Below is a very simplified version of some code that I'm passing to Google Closure Compiler:

"use strict";

var xhr = new XMLHttpRequest();

xhr.open("GET", "somefile", true);
xhr.responseType = "arraybuffer";

xhr.addEventListener(
  'load',
  function() {    
    var data = new Uint8Array(xhr.response);
    /* ... do something ... */
  }
);

This is basically an Ajax query to retrieve raw binary data and it is working as expected.

However, the compiler emits the following waing:

WARNING - actual parameter 1 of Uint8Array does not match formal parameter
found   : *
required: (Array<number>|ArrayBuffer|ArrayBufferView|null|number)
        var data = new Uint8Array(xhr.response);
                                  ^

I've spent some time trying to fix it with JSDoc directives, in order to explicitly define the type of 'xhr.response' as 'ArrayBuffer'.

For instance:

/** @property {ArrayBuffer} response */
var xhr = new XMLHttpRequest();

But nothing worked.

What DID finally work was to separate the variable declaration from its initialization, without adding any JSDoc directives:

var xhr;
xhr = new XMLHttpRequest();

No waing anymore.

The problem is that I don't get it. Why does it fix the problem? Was it really the correct thing to do?