When I try to save a replay file while it has a preset camera path will cause it to hang while spamming this to the console: http://pastebin.com/zjRMkAsJ
I have tried it with and without optifine, but it doesn't work, even with only two time and position keyframes.
I tried this 3-4 times by going into a replay, placing two time and position keyframes, saving them, and exiting the replay.