I have a problem with actionscript 3, especially when using the embed tag. I have this code:
[Embed(source = \"sound.mp3\")]
private static var soundClip
The Embed process implies a transcodification (made by the compiler), if the sound doesn't fit into the supported Flash Player Sound format you can get unexpected results, like shrunk length. Check that the sounds you embed is at 44100 Hz Stereo, that is the supported sampling rate that won't cause any issues.
Cheers!