Ok, I see what's up. When the integrated audio code was added, the path was not set up to compare all lower case (bad, bad programmer). Try this as a workaround - For the playback audio path, put this in:
{TXTLOWER:Musique_en_cours}
instead of {TXT:Musique_en_cours}
The lower case issue has been fixed and will be out in the next release. However, when I do this with Windows Media components, I'm not able to reproduce the problem and I'm able to get the position each time (no code change).