I have a client that spent big bucks on a single word domain for a term. Lets just say "screws" is both the domain name and term for a search in his nitch. A recent development in his area nitch is not related to screws as we think of a screw, but is a term the industry uses to describe the job within this industry.
Searching G right now for screws brings up what you would expect screws and types of screws. He built a solid site in the domain "screws" added good content, videos, pictures and technical data about his company doing "screws" for this industry.
In adwords we added the keyword [screws] and it comes back a 1. So we added [company screws services] 7 and so forth. All scores are good except "screws" and or "screw". I told him to delete the term "screws" until Google can figure out there is another industry that uses the term "screws". I figure the bot just for now only reconizes the term in one industry and looks for realted content within that specific industry. Not finding content related to this industry it kicks it out and applies a real low score. His adwords ad, domain name, and related content for this term should be a 9 or 10 but ends up a 1. First time I have ever had a 1. Live and learn I guess.
buck not doing any broad search terms at all on this site. All are in  Just looked at some terms I added last week they are popping top 1-2. Single terms are still 1 or 2. Got to be the nitch is dominated by companies selling different types of screws and with the content on the site not about what we all think are screws the bot is doing a behavioral grading and giving these terms a failing grade. With the new changes I guess your right on the negative keyword terms After thinking about it. Will keep an eye on the account and see. I just paused the term just so I can continue to watch the grade on these terms.