scout - 2:05 pm on Jun 10, 2008 (gmt 0)

Searg, watch your match types. You may be experiencing an issue where Yahoo is mapping search queries to your obscure advanced match keyword because it has a higher max cpc then a similar keyword. If you experience a sudden impression increase on an obscure long tail keyword, chances are it's a mapping issue on advanced match or a yahoo syndicate, or even both.