IMDB keyword search

I was trying to identify a film that I had seen it in a jetlag daze at 5am once, and could remember little about it, except it was opera-style and about cowboys.
 
So I went to IMDB, to their keyword search and typed "cowboy opera". I spent some time trawling through the results, but I couldn't find it. So then I spent a lot of time using other ways of searching for it (an actor whose name I didn't know had played in it, but I had seen another film that he had played in whose name I also didn't know, but I did know the name of an actress in that film, so ... you get the picture).
 
I eventually found it. It was called Horse Opera. I looked at the keywords, in order to fix them, and guess what? It has exactly three, Cowboy | Opera | Opera Commissioned For Television.
 
So I decided to try and work out why I had failed to find it via a keyword search. I tried searching for Cowboy, but Opera wasn't in the list of related words next to it. I tried searching for Opera, but ditto. I tried to find a way to narrow down a keyword search with another keyword that you typed in, but there didn't seem to be one.
 
Then I noticed that the URL for a keyword search (after you had clicked on a result) was http://www.imdb.com/keyword/cowboy/
 
So as an experiment, I changed the URL to http://www.imdb.com/keyword/cowboy/opera/ and guess what! One result, the film I had been searching for!
 
There is clearly something wrong with IMDB's keyword search!