When I change the audio output sound level in Comcast Video Mail, it also changes the sound level on the audio slider in Windows. However, when I close Comcast Video Mail, my Windows audio slider returns to its previous setting. Why?

By design, Comcast Video Mail is programmed to change your Windows audio output settings to the appropriate place for you to be able to hear comfortably when using the program. When the program closes, it returns your Windows audio input slider to its original setting for you.