What is causing my scripts to be requested twice while using Modernizr.load (yepnope.js)

Question

I am using yepnope.js to load javascript files dynamically,and I've noticed that my scripts appear to be loaded twice according to Firebug and Webkit Inspector.

The problem is that in Firebug's Net panel (Firefox 4 latest), their response is a 200, not a 304. It seems to be slower than in Chrome.

I have uploaded this video showing the issue. You can see how the files jquery-1.6.1.min.js and libs.js are loaded an extra time.

The code I am using to do this is the following, simplified:

Modernizr.load({
                load: ['jquery-1.6.1.min.js', 'libs.js'],
                complete: function () {
                    console.log("loaded");
                }
});

Modernizr.load() is yepnope().