Another episode of "fixing that stupid map edge bug again".

code/game/atoms_movable.dm

@@ -31,6 +31,7 @@
 	var/atom/movable/pulling
 	var/grab_state = 0
 	var/throwforce = 0
+	var/can_be_z_moved = TRUE
 
 /atom/movable/vv_edit_var(var_name, var_value)
 	var/static/list/banned_edits = list("step_x", "step_y", "step_size")

code/game/turfs/space/space.dm

@@ -134,7 +134,7 @@
 	if ((!(A) || src != A.loc))
 		return
 
-	if(destination_z && destination_x && destination_y)
+	if(destination_z && destination_x && destination_y && !(A.pulledby || !A.can_be_z_moved))
 		var/tx = destination_x
 		var/ty = destination_y
 		var/turf/DT = locate(tx, ty, destination_z)
@@ -157,8 +157,10 @@
 		A.forceMove(DT)
 		if(AM)
 			var/turf/T = get_step(A.loc,turn(A.dir, 180))
+			AM.can_be_z_moved = FALSE
 			AM.forceMove(T)
 			A.start_pulling(AM)
+			AM.can_be_z_moved = TRUE
 
 		//now we're on the new z_level, proceed the space drifting
 		stoplag()//Let a diagonal move finish, if necessary