Changes

diff --git a/scripts/main.js b/scripts/main.js
index 8df176b..8f3bbee 100644
--- a/scripts/main.js
+++ b/scripts/main.js
@@ -1,6 +1,6 @@
 const DEFAULT_APP_STATE = {
     floor: 0,                   // This is 0-based.
-    plan: new Array(FLOOR_COUNT).fill(
+    plan: new Array(FLOOR_COUNT).fill(null).map(() =>
         new Array(GRID_SIZE_X * GRID_SIZE_Y).fill(0)),
     // mouse_state can be “normal”, or “dnd”.
     mouse_state: "normal",