If you've been paying very careful attention over the past week, you may have picked up on a temporary glitch that caused old crates to produce unusuals 100% of the time. You can read Valve's writeup and solution here.
On Marketplace.tf's side of things, we were lucky enough to have shut down all services about 1 hour into the event, but within that timeframe, some users managed to sell some of these "glitched" unusuals to buy orders made on Marketplace.tf. To that end, we will be refunding in full any buy order filled with a "glitched" unusual. This is about 150 unusual hats that we will be refunding. Some users who sold these unusuals to buy orders have graciously agreed to return what they earned through them, but this is a minority of the unusuals; the majority will be refunded by Marketplace.tf.
While we are not responsible for Valve's mistakes, we could have done more to prepare for such an event. We will be instituting safeguards moving forward to detect similar anomalies, as well as providing safety features for those who create buy orders -- such as the ability to set a limit on the total amount spent by your buy orders within a 24 hour period. We'll let you know when this goes live.