Okay, this is due to WMM being a laggy bitch. It's not the audio, and it's not the clips. WMM does it to me a lot of the time, especially with my latest one that uses a lot of spliced and timed clips. It can get off track.
It's nothing much to worry about.
Just save your progress, and close down WMM completely. Now, wait a few minutes, and then go back to WMM and start it up again. It'll be fine.
It's also a good idea, sometimes, to log out of your account completely, and then log back in. If this is a hobby that you're serious in, I would suggest staying with WMM for a while, and getting used to it, before going to a different program like Vegas, Adobe, or Cyberlink. There's a lot of things that you can do in WMM if you just take the time to be creative- and not get upset over its laggy old self.
If it's not something you're really serious in, then don't waste the money or try and illegally download it.