This has happened to me twice now where I cast fairy dust on an AI champion who is in a poison cloud and it seems to cause the AI to crash for that turn. It will do nothing until the 10 minute timer will expire and then everything will be fine as far as I can tell. The next chance I'll get I'll see if it happens w/o the poison cloud. But twice in a row seems to indicate something if just bad luck Edit: Yep, at least on my system it's confirmed that causing an enemy to have wandering in a poison cloud will cause the AI to lock up. Now to test w/o the cloud. Edit 2: Wandering alone doesn't seem to cause it, it needs to occur in a cloud.
Thank you for posting this. We have been hearing about this issue, but to have a reproduction step is extremely useful.