Loading .obj file with OBJMTLLoader.js

Question

In Three.js I'm using OBJMTLLoader.js to load my 3D model.

After Chrome has loaded the scene, the model is not shown. In the console I have >60'000 warnings. They all look like:

THREE.OBJMTLLoader: Unhandled line f -215//-215 -202//-202 -212//-212

When I use OBJLoader.js to load the model (without the .mtl file), the model gets loaded successfully (of course without materials)

What is the problem with the OBJMTLLoader.js loader?

This is how I load the model:

<script src="scripts/objmtlloader.js"></script>
<script src="scripts/DDSLoader.js"></script>
<script src="scripts/MTLLoader.js"></script>

...

THREE.Loader.Handlers.add(/\.dds$/i, new THREE.DDSLoader());
var loader = new THREE.OBJMTLLoader();    
loader.load(objFileName, mtlFileName, function(object) {
    scene.add(object);
});