Adsense publishers may have a page(s) that relates to your keywords which triggers your adword ad to show. Now, when that page is spidered, your ad is also included. Do a search for some of your KW-KP and you may find that top SERPs are large content sites that have been 'adsensing' your ad while being spidered.
Very easy to see a loss in sales, as naturally the content of the publishing site is directly related to your adwords campaign and such a site could provide links to competitor site(s) and or product(s).
Furthermore, your ad(s) may not appear on these sites after they have been listed in the SERP, as your campaign has been changed. This may in fact cause a listing to continously rank higher than you until the page(s) are updated in each of the SE's.
[edited by: KoDe_GuRu at 1:05 pm (utc) on Feb. 1, 2004]