Hmmm....
Ok... at first I couldn't (didn't remember the specific steps), but then I was able to.
I created a new smartplaylist, created a search item, clicked on all music, and the terms disappeared, but the area was blank.
I was also able to recreate by clicking Edit on a smart playlist, clicking in the search field, and then clicking all music.
Posting from a different computer, but I'll have a screen shot posted shortly.

- Edit: Screen shot attached. You can see the 'blank' portion of the screen at the bottom of the track list.

Screen Shot 2012-12-17 at 11.46.03 AM.png
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