Most likely just the system re-adjusting invalid or miscounted clicks...like sometimes the same person will click back on a link and then click back thru..shows two clicks but it's really just one on the same ad, etc
Actually it's Yahoo not liking the source of your clicks. Sad but true. No matter how valid a click might be, if Yahoo doesn't like its source (e.g. from countries far from the country of origin of the advertiser) they won't pay you for that click.