I am not 100% sure why this happen but what i am guessing is that when a wendy leaves with abigail out the game doesn't know where to store the abigail and therefore loses connection (it does not crash the game, it simply makes it lose connection) which is unfortunate since it doesn't save when a player leaves (which is understandable knowing griefers) but it is mildly annoying to have to redo stuff from when the game last saved.
I hope this gets fixed because it can become something that griefers realise and use to mess people over, which is not very fun.
join a world
use a character
have a wendy join
let the wendy spawn abigail
have the wendy leave, (you may need to be close by for it to work)
you just lost connection to the world, even as a host