"files" parameter fails when wildcard or array are used

[Parka]

For the following task:

 audiosprite : {
        all : {
            output: "./app/assets/audio/",
            files: "audio/*.wav",
            export: 'm4a,ogg,mp3',
            bitrate: 48,
            silence: 5
        }
    }

This is the output:

Running "audiosprite:all" (audiosprite) task
>> debug:Parsed arguments _=[audio/*.wav], output=./app/assets/audio/, o=./app/assets/audio/, export=m4a,ogg,mp3, e=m4a,ogg,mp3, bitrate=48, b=48, silence=5, s=5, priority=, y=, loop=, u=, log=info, l=info, autoplay=null, a=null, samplerate=44100, r=44100, channels=1, c=1, rawparts=, p=, $0=node c:\xampp\htdocs\gamedev\phaser\test002\node_modules\grunt-audiosprite\node_modules\cloudkid-audiosprite\audiosprite.js
>> debug:Created temporary file file=C:\Users\parka\AppData\Local\Temp\audiosprite.7499742431100458
>> debug:Spawn cmd=ffmpeg -version
info: Silence gap added duration=6
>> debug:Start processing file=audio/*.wav

>> Exited with code: 1.

Warning: Task "audiosprite:all" failed. Use --force to continue.

Using:

files: ["audio/*.wav"]

Returns:

Running "audiosprite:all" (audiosprite) task
Warning: Cannot use 'in' operator to search for 'src' in audio/*.wav Use --force to continue.

Aborted due to warnings.

This works ok:

files: "audio/interface6.wav audio/metal-ringing.wav audio/swing.wav"

I don't know how relevant it could be but upon installation of audiosprite I get the following warnings (I'm sorry for the image, idk how to dump that log):

Additional data:
Windows 8
Node v0.10.31

[stevebma]

I have this on windows only, on linux the wildcards work fine.

[GMartigny]

Had it on Linux

error:
Warning: Cannot use 'in' operator to search for 'src' in src/audio/**/*.wav

options:

audiosprite: {
        main: {
            files: ["src/audio/**/*.wav"],
            output: "dist/audio/",
            export: "ogg",
            ogg_to_oga: true
        }
    }