PowerPress uses the duration value for the iTunes duration tag in the RSS feeds as well as optionally display the duration on the web page for web visitors. It doesn't pre-populate values in Flash, none of the Flash players we've tested allow you to specify the length.
I'm not a Flash developer, so don't know the technicals why the mp3 duration keeps changing in flash. I do know that the flash player itself detects the duration by first looking at the ID3 tags (tags with media information inserted into the beginning of the mp3 file) in the media file then by scanning the entire file length. mp3s are interesting, they are a compilation of frames of audio. The ID3 tags tell the application what the sample rate is, how many frames there are, bit rate, length, etc.. and the application can then determine the duration from that information. The exception happens when some frames that are inserted into the audio use different bit/sample rates, in which case the actual duration will change once the player scans that portion of the file. A good portable MP3 player will scan the entire mp3 before displaying the duration. Flash is trying to be efficient by allowing you to play the audio before the entire file is downloaded.
You can learn more about mp3s here:
http://en.wikipedia.org/wiki/MP3It most likely wasn't flash but the problem was that the mp3 did not entirely load in the player when you had the play stop issue. I still recommend folks upgrade flash to give them peace of mind.
You can use a different player, the WP Audio Player (
http://wpaudioplayer.com/) is actually what PodPress uses and works well in PowerPress. Just disable the PowerPress player and configure the WP Audio Player. WP Audio Player settings are confusing, so just take your time going through them and make sure you allow it to add a player for enclosures/podcast episodes.