This is an old Yahoo (Overture) trick to increase revenue.
Years ago I complained to them when a keyword that hadn't reached 100 impressions in months suddenly had 1000s.
It was the same thing - they had put the keyword on the front page. It cost me a lot of money for those days.They wouldn't consider a rebate for these useless clicks. I have never trusted them since.
The basis of my thinking then & now is that we pay for "Search Engine" clicks. If we wanted "content" advertising we would do so.
"Search Engine" implies someone with interest is specifically searching for your product or service. If it's plastered on the front page of a huge portal this is NOT a search engine click & is fraudulent.
The people running PPC in Yahoo are inherently dishonest & have been for years.