It's a Coinbase transaction and not a Bitcoin transaction that's at issue.

It looks like Coinbase has a problem managing their float of Bitcoins and/or serious risk management problems.

There was a story yesterday about someone wiring over tens of thousands of dollars and not hearing back for 1-2 weeks.

My theory is that Coinbase are performing some kind of proprietary trading and have burnt themselves badly, and to recover losses, they are front-running customers and delaying trade settlement.