Optional Search Terms filter displays no results despite being optional, unless blank key query set in url

I am trying to make a simple search/browse listing for a site. The idea is that the default listing shows all instances of a content type, but an exposed search filter box at the top allows users to optionally narrow down the listing.

However, unlike other exposed filters which are set to optional, the search terms filter seems to work differently. If the filter key is not part of the url, it shows no results, instead of all results.

I have exposed the search terms filter, and made it optional. I _want_ all results to appear when nothing is entered into the search terms (which is the case when someone goes to the base url).

The behavior I'm getting though, is that if someone goes to the base url, without the search tag entered, it shows no results. If the query tag is appended to the url, but is left blank, it behaves properly (showing all terms).

So, for instance...

http://www.nameofsite.com/browse/recipes

... results in no results, while ...

http://www.nameofsite.com/browse/recipes?keys=

... shows all results.

This is not the way the other filters seem to work.