Problem using spectral editing tool using Audition CS5.5

When I try to delete certain frequencies using the spectral editing tool, all the other audio disappears as well. I've seen this method demonstrated in a number of videos, and as far as I can tell, I'm doing it correctly. If I play the selected are before hitting delete, all I hear are the selected frequencies, so I assumed that's what I'd be deleting. After hitting delete, the selected area goes gray and the rest of the clip looks normal...but I hear no audio. Any guidance would be greatly appreciated!