Option to leave group chat has disappeared?

Hello everyone. I understand that iOS 8 introduced the ability to leave group chats by tapping "details" and scrolling down and tapping "leave conversation". At first after I updated to iOS8, that option was there. Now it isn't. Other iPhone participants in said group chat (consisting of a mix of iPhones and other phones) have said that they can't find the option to leave anymore either. Why is this? I know you can disable group chats in the settings, but that's not what I want.