diberry - 2:58 pm on Jun 1, 2013 (gmt 0)
I had almost exactly the same situation, even down to changing the URL and not redirecting. It's a Penguin thing, and several other people saw similar stuff - take out one word from the keyword phrase, and the page comes up, or add the site name to it and it comes up, etc. It's like my page has been penalized for a single word.
I had initially deleted a lot of outbound links from the page, thinking maybe Google saw it as a link farm rather than a resource page. I left that change in place, but later returned the URL to its original state.
The page has not fully recovered since Penguin, but it did come up several hundred spots and continues to creep upwards. I may never rank for it again, and I don't know whether that's because I didn't know the right things to do or because part of Penguin IS never letting you rank for that phrase again.
Hope this is somewhat helpful!