tedster - 3:44 am on Oct 1, 2012 (gmt 0)
This pattern (not finding a particular uncommon phrase) is something that has affected a few sites over the past year. It's not very common, but it's common enough to know that it's a kind of pattern.
What creates the pattern is the question for me. I wonder if it's an intentional filter, a kind of manual action to generate only partial indexing, or an unintended data bug.
I've seen the situation clear up in a couple cases - so please let us know if you see any changes, or get any insight into what's going on in your case.