Just so you know Madshi, that German audio track from Mozart - Die Zauberflote encoded just fine with -nero. So I guess libav is to blame. Though I ended up scrapping the encode, because after 230000 frames, I realized I forgot to tell it to deinterlace since it is 1080i content; I used the framecount from evodemux and it was short about 60000 frames; adding a .srt file to my MKV started having WMP asking for xvidcore.dll; and it seemed the audio was out of sync significantly. As in, I couldn't even tell what scene I was hearing because it was nowhere in the vicinity of the video (even at the beginning).
So I scrapped that movie as a conversion entirely
Thanks for continuing to answer my - and others' - questions!