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At http://people.xiph.org/~xiphmont/demo/celt/demo.html there are two WAV files in audio elements. If you play both of the elements using their controls simultaneously a few times, eventually you'll not be able to replay the first one.
1. Load http://people.xiph.org/~xiphmont/demo/celt/demo.html
2. Scroll down to the section "Why low delay?"
3. Play "Sample 1" and "Sample 2" approximately simultaneously by clicking on the elements' play buttons in quick succession. Once both elements have played to the end, repeat a few times.
4. Try to play "Sample 1" by clicking on its play button, it may not play (if it does play, repeat step 3 a few more times).
The audio elements are playing WAV files, not Ogg, so it could be the case that there's an event the videocontrols are exepecting that the nsBuiltinDecoder backend sends that the nsWavDecoder isn't sending.
I can't repo using today's nightly.
nsWaveDecoder was replaced in bug 635649, and I can't reproduce this in a current build.