ID:1835573
 
(See the best response by Lummox JR.)
I don't get whats wrong I try to put down a turf ontop of another turf like normal but its deleting the turf below it for no reason i changed the click instance aswell and both things have no affect yet the other turfs are on the map are fine yet when i try to place turfs it deletes them why?

Best response
If you were used to map editing before BYOND 455, we changed the way the map editor works so now it's (IIRC) Ctrl+click to make the old turf an underlay. However you can change this behavior in the menu.