Hey Duncan Dam and jwfitt-
We are aware of this issue and are working on it. I have added jwfitt to this post as well as you both were having a very similar problem. Just to confirm the State Machine you are trying to copy does it have State Event nodes inside of it and are your pasting it directly to the AnimBlueprints or inside of a newly created State Machine. A screenshot of the blueprint right before you CTRL-V (paste) and teh editor crashes would be helpful.
Thanks Guys -
Eric Ketchum