Just an update since there does not seem to be a 2014 thread on the subject: But, I just tried to buy a few BTC using Coinbase near the bottom just after Bitstamp announced their fix. So, of course Coinbase canceled the transaction as "high risk" after the price went back up. So, take it for what it is, more of the same...
It's simple, if you ask me. When price goes up. They cancel and take the profit. If it goes down, why cancel when it won't make them money. That's why regulation is vital for these companies. If regulated, they won't be able to come up with this crap.