https://gist.github.com/yrsegal/4f9ca65d13b74dbf69dea24e6a9d548a
This occurs approximately 3 times out of 4 loads of the game. By stepping through with breakpoints, it appears that the resize behavior for ListenerList, meant to keep it consistent across all listener lists, was not resizing the last 14 or so out of about 50 listeners. This leads to a crash (ArrayIndexOutOfBoundsException), as seen above.
I have confirmed, by putting locks into the code, that this does not occur if the setup threads are not concurrent.