You're right, J7N - I checked it right now - when "bad" FLV started playing, FFDshow (with FLV splitter) didn't launch, and when I looked into filters, MPEG Layer 3 was used. You can see it in the image below
Unfortunately changing the priority of the filters didn't work. I tried to set FLV-related filters (FLV source, decoder and splitter) as high as possible and even disabled mp3 filter, but the only result was that another audio filter got to decoding (Nero Audio...). Is there any way how to force BSPlayer to decode FLV files with proper filter?