To your point Praxus, you're absolutely correct. It does seem unlikely that there is a secret quality smack down happening. I'm being a little "tinfoil hat" and possibly jumping to conclusions. It just doesn't make sense to me that the same keywords, at the same bids would get significantly less volume with bing, yahoo, and the partner network under one umbrella than bing separate from yahoo and their partner network.
There is definitely truth to the differences in adcenter vs yahoo match types. Advanced match cast a much wider net than adcenter's broad match. So you definitely lose impressions moving from one to the other.
I believe groupM or efficient frontier did a large scale study on the implications of CPC increases once the integration happened and predicted CPCs would go up short term.
All said, this issue boils down to the following.
1. loss in volume to keyword gaps caused by match type differences.
2. loss in volume due to CPCs being higher, thus creating a higher barrier to entry for the auctions (both on Bing/Yahoo and the partner network).
3. Some sort of technical glitch with ads not being served.
4. A budget pacing issue.
5. A secret editorial penalty (unlikely, but still worth mentioning).