symfony: guessExtension() return the wrong mp3 file extension

i have this code, which i use in laravel 4 to upload and validate a file ( and they assure to me that this is related to Symfony HttpFoundation https://github.com/laravel/framework/issues/1968#issuecomment-21720088 )

<?php
class HomeController extends BaseController {
    public function getIndex()
    {
        return View::make('hello');
    }
    public function postAddFile(){
        $file = Input::file('pod');
        $files = array('file'=>Input::file('pod') );
        $rules = array('file'=>'required|mimes:mp3');
        echo 'File : '.$file->getClientOriginalName().'<br />';
        echo 'Mime : '. $file->getMimeType().'<br />';
        echo 'Ext : '. $file->guessExtension().'<br />';
        $validate = Validator::make($files,$rules);
        if($validate->passes()){
            echo 'Mime : '. $file->getMimeType().'<br />';
        }else{
            var_dump($validate->messages());
        }
        $file->move(storage_path().'/cache', $file->getClientOriginalName());
    }
}

which am use to validate the file which am uploading … but sadly the result is this :

File : test.mp3
Mime : audio/mpeg
Ext : mpga
object(Illuminate\Support\MessageBag)#151 (2) { ["messages":protected]=> array(1) { ["file"]=> array(1) { [0]=> string(37) "The file must be a file of type: mp3." } } ["format":protected]=> string(8) ":message" }

as every one see the validation failed to read the extension of the file, and the result of the $file->guessExtension() is mpga mean while it should be mp3 …

so am not so sure what is the problem here, and if this is something related to php configuration … my server is ubuntu with php 5.3