Trance,

Sorry for the confusion here. We use machine learning algorithms to prevent fraud and they're not always 100% accurate. If you feel you've had a transaction cancelled incorrectly send support an email. We regularly review transactions and push them through at the original purchase price upon request. I also wrote a bit about our fraud program in the fourth section here:

http://newsbtc.com/2013/11/07/coinbases-olaf-carlson-wee-answers-questions-users-technical-issues/

Hope that helps!