Happens to me too. I tried to monitor it and what I have found is that Minecraft for some reason consumes ALL the RAM when the chat bug is happening, making the computer freeze as it has no more RAM to use.
I'm also experiencing this x-x. Very inconvenient and unpredictable. You don't know if the game will decide to lock up or not :/
What's the processor of your systems? Since it happened on an AMD in my case, what are yours? Maybe we can narrow the cause down while we wait