New keyword density filter at work?

[Soze]

I did a search for keyword1 keyword2. I have an entire page dedicated to this keyword phrase. It used to be #3.

Now it is like 15 and the listing shows my root domain and another page, which each only mention this keyword phrase maybe once.

What, other than some type of filter, would cause two pages that mention the keyword phrase only once to outrank the page optimized for the keyword?