Saving Vorbis audio from WebM results in bad file?

[Cormy1]

I have a WebM Video with Vorbis audio. I load it into Avidemux, click "Save Audio" and it creates a dialog to save the file as filename.* under All Files
When I save it as filename.ogg as it is Vorbis audio, I get a file which cannot be played by my media player.
However if I run ffmpeg -i filename.webm -map 0:a -c:a copy filename.ogg I get a working file, with roughly the same filesize as the one produced by avidemux (153MB from ffmpeg vs 150MB from avidemux)

[eumagga0x2a]

We cannot create Ogg containers yet, so no working Vorbis export. Patch welcome.