100% survival only game, wife just got achievement for getting to the end as proof

at the time of the glitch my wife and i were split screen 2 player going to the end and about to take a second attempt at killing the dragon. i had prior to this made probably 10-15 run and deaths to the end breaking the heal beam things. 

so we did the first attempt he agroed while we were in the ground, we got out and killed us. we re-spawned my wife afk'ed in the neither tunnels i made and i had ran back to the end. once getting there i heard a strange metal clanging noise for about 10 seconds and then i did-int see the dragon any more was shortly after killed by endermen. i got teleport-ed back and notice a huge hole in the side of the house and now the dragon was here in the normal world.

it cleared a huge pit down to bed rock and blew up about 1/3 of the house with full chests of stuff. 

it then after about 10 mins of this and us trying to find where the arrows were we took some shots at it but it disappeared. i went back to the end and it was also not there. the fountain portal was active so i assume it bugged out and died however now for the second time ( we restarted cause the dragon de-spawned in the end once before) and i still dont have my achievement for the kill and this thing ruined our game its completely unplayable with the amount of damage it did. i have no idea what caused this. 

this game really needs to have a option to control the world saves so people can try to roll back to pre bug states my wife is fuming shes so mad this happened and we will probably have to restart once again. 

ill leave my game in this state if someone wants some screen shots or something. cant believe this happend