Sony Vegas 7.0 mutes audio upon normalisation command?

[2prfm.com]

I've imported a DVD buy using the import Camcorder/DVD option in the file menu. All the videos loaded successfully into the "project media" folder.

I've dragged the first clip onto the story board, and as can be seen in the first shot, all looks fine with the video and audio.


[Attachment 2885 - Click to enlarge]

When applying right click>Switches>normalise, the audio wave signal turns into a flat-line, meaning that it has been muted.


[Attachment 2886 - Click to enlarge]

Just wondering why it would mute, when I've used the normalise command?