On my iPhone 5s, sometimes I will finish typing a message in iMessage and hit "send." However, the "send" button simply doesn't work no matter how many times I press it. Everything else is responsive and fine. I can still type/delete etc etc. Just can't send. However, if I flip the phone to vertical mode, the "send" button magically works again. Running the latest version of iOS 8. Any idea what's causing this or how it can be fixed?