One of the new features of iOS 9 that Apple hasn't actively advertised has the tremendous potential to be actively used on an everyday basis by the vast majority of users: it at last permits third-party developers to implement Quick Reply functionality within banner alerts, the Notification Center and notifications shown on the Lock screen.
Twitter is one of the first applications out of the gate to have readily adopted this feature in its most recent update that just hit the App Store. And if you own an iPad with iOS 9, you can now use Twitter in iOS 9's new side-by-side multitasking mode.
People are reporting on Twitter that Quick Reply is broken in this update and a few members of our team were able to independently confirm this.