Search Improperly strips out Category

first, visit this url: http://drupal.org/search/node/category%3A14+image

you will see the search terms 'image category:14' appear in the search field, If you just hit the search button again, you will find that the category:14 is getting stripped out.

however, if you change the : in the search field to %3a and hit search again, it will NOT strip out the category