Suppose you are trying to connect to a Minecraft server. At the Connecting to server..." and "Logging in..." screens, the "Cancel" button is at the bottom of the screen, just like normal, as shown in my attached screenshot titled "Bug31.png". However, if you get an error, the "Return to title screen" button will move up underneath the letters, as shown in "Bug32.png". In that example, the error is that the server is too old, but it should give you that with any error.
Confirmed for
15w36d