That's really odd. That should just remove results that match the "ai" keyword according to google's search syntax. Messing around with it, it looks like google just doesn't provide summaries for queries using search operators.

So you could actually add a meaningless negative keyword and be good to go, like "-asdfasdfasdfasdfasdfasdfasdf". Should get nearly the same results without removing results that might happen to contain the letters "ai".