Must be your IE because I select this fine using Mozilla I use or my IE 7 that is shipped with my Vista Operating System. Seems tied to with your browser and not the code as I can not replicate with the IE 7 browser. I am using IE 7 7.0.6000.16368
http://www.reeftalk.com/gallery/search.php?searchid=46
This is a multiple cat search on the same keyword blue using like 4 cats( corals through fish). I get 11 results. Search all gets 14 and searching corals get 4 which was my initial example above.
By the way you use SHIFT not CTRL