I tested an app yesterday that my team is working on. It has a hamburger navigation, and one of the items inside that nav is a callout to leave feedback. When you tap the feedback row, a modal screen flies in from below, and you get your feedback form.
Here's the problem. The only way to get out of the feedback form without leaving feedback (if you leave feedback, it's dismissed) is to tap the device's 'back' button. There's no way to dismiss it from within the view without leaving feedback. Is this a usability issue? I'm a strong believer that you shouldn't rely on the device's hardware buttons, but I can't find anything to back me up on this.
I've attached a very basic version of the functionality to show you guys what I mean.