Several reports from users testing the latest leaked build of Windows 7 indicate a potential data corruption issue using Microsoft's Windows Media Player 12.
Windows 7 beta 1 build 7000 leaked over the Christmas holidays and a Microsoft spokesperson has confirmed that there is a bug which affects the leaked build. Approximately 2-3 seconds will get shaved off the beginning of MP3s if you have set your Windows Media Player 12 settings to retrieve information from the internet and update files. The default configuration for WMP12 sets this if you use the "express" option during setup.
"The problem only happens when you edit metadata on a certain class of MP3 file (a file with a header larger than 16KB). When the new metadata is written, it corrupts the beginning of the file. This can happen either when you edit the metadata from inside WMP or Explorer, or it can happen if you have WMP set to automatically fill in missing metadata using the online service and add the MP3 to your library. This problem is only present in the recently leaked build" (7000) according to one poster in our forums.
Microsoft's official response is "Microsoft is aware of this issue and it will be addressed in the beta program". The company is currently hard at work readying a QFE (quick fix engineering) patch that will be distributed by Windows Update for those with official and non-official access. A support (KB) article is expected soon.
This highlights the importance of not using leaked builds with any applications or data that is critical and waiting for beta builds from official channels. We expect Microsoft to stress the urgency of applying the QFE patch to those in the beta program.