The EVENT_GROUP_CHANGE triggers when a client joins or leaves a group or raid. It isn't a heavily useful event, but it might be something that a server with Bots could find use for on occasion. Though, since it only goes to player.pl, I don't know if a bot would even show up or not.
Also, here is another mention of corrupt stack with #mystats:
http://www.eqemulator.org/forums/sho...751#post195751