/newisland replace not working

I have been away a couple of months and i felt like starting over. When i do /newisland replace something strange happens, a new island is generated on top of my old (and rather large) island. I dont want to go around and dismantle it by hand! I tried it twice, and both times i then confirmed with /newisland yes. Is there something else im missing here??

 

Okay nevermind! i guess it doesnt work when i type it from spawn, i needed to be ON my island when i did it. (i was worried id fall through the earth or something if i did it while i was home)