Well - the sound in question *is* stereo, there's a comment in the code saying that by this stage is should be been converted to mono but I'm not familiar enough with the sound code to know where that's supposed to happen. Given that it's the afterburner sound that triggered this, if it were a straight-forward bug you'd have expected it to trigger a lot more than just in M6.
As for OpenAL, I've mostly been using 1.13 and I'm not aware of any issues with 1.14. Some of the error handling (or something similar) has changed between the versions though, I know that 1.14 logs some errors on start that I don't get with 1.13.
@sixsixfive - is OpenAL 1.13 available in the debian repos and would you be able to try using that instead of 1.14?