Fast User Switching MediaPlayer will keep on playing with sound

We found one issue need your help. When we Fast User Switching from One to
another, MediaPlayer will keep on playing with sound... MediaPlayer will keep
on Playing but Media Center will NOT. We are not sure it's Vista problem or
App SPEC.. Please reference following steps:
1. Create A and B account in Vista. No matter Limit or Adm.
2. Log-in A and play music by MediaPlayer.
3. Fast User Switching to B.. But We still can hear the sound from A
account.. --> Different from XP.
4. If we use Media Center to play Music, then it will Stop as XP..