jecasc - 3:37 pm on Jan 12, 2011 (gmt 0)
I have encountered strange things with my internal search in the past. Google Bot tried random keywords from my websites and used them as search strings in my search form.
I first thought someone must be linking to my website and Google would only follow, but this was not the case. The crawler used random words from my website and submitted them.
Are the keywords unrelated to your website or do they appear somewhere on your website? If they appear on your website than it is probably this.