Personally, I don't think they did it on purpose. You probably hit some threshold of fiat movement that triggered additional AML/KYC.
I recently got my google wallet frozen and was requested for bank statement of the same bank that was linked to my account. I've done a handful of transactions without any problems using the same linked bank, then all of a sudden my account was suspended and all pending transactions were canceled. Wasn't a huge deal to me, I just uploaded ID and docs and got my account back a day later.
This exactly parallels what happened to you, except my Google Wallet account had nothing to do with BTC, so google had nothing to gain from doing that. It was just to verify that my funds had been going to the correct account this whole time.
I agree that it was
likely unintentional.
The fact remains that a trade was rolled back hours after it happened, as a result of a mistake/bug on their part. I still haven't heard back from them and this incident happened early this week. Coinbase's support is first-class compared to this.
