diff -r d41833895448 -r 28cc45444d44 minesweeper/src/main/java/org/apidesign/demo/minesweeper/MinesModel.java
--- a/minesweeper/src/main/java/org/apidesign/demo/minesweeper/MinesModel.java	Fri Feb 07 17:22:58 2014 +0100
+++ b/minesweeper/src/main/java/org/apidesign/demo/minesweeper/MinesModel.java	Fri Feb 07 20:22:14 2014 +0100
@@ -77,7 +77,7 @@
             return name().startsWith("N_");
         }
 
-        final SquareType moreBombs() {
+        final SquareType moreBombsAround() {
             switch (this) {
                 case EXPLOSION:
                 case UNKNOWN:
@@ -121,8 +121,10 @@
         List<Integer> yBombs = new ArrayList<Integer>();
         final List<Row> rows = model.getRows();
         boolean emptyHidden = false;
+        SquareType[][] arr = new SquareType[rows.size()][];
         for (int y = 0; y < rows.size(); y++) {
             final List<Square> columns = rows.get(y).getColumns();
+            arr[y] = new SquareType[columns.size()];
             for (int x = 0; x < columns.size(); x++) {
                 Square sq = columns.get(x);
                 if (sq.isMine()) {
@@ -130,7 +132,7 @@
                     yBombs.add(y);
                 }
                 if (sq.getState().isVisible()) {
-                    sq.setState(SquareType.N_0);
+                    arr[y][x] = SquareType.N_0;
                 } else {
                     if (!sq.isMine()) {
                         emptyHidden = true;
@@ -142,7 +144,17 @@
             int x = xBombs.get(i);
             int y = yBombs.get(i);
             
-            incrementAround(model, x, y);
+            incrementAround(arr, x, y);
+        }
+        for (int y = 0; y < rows.size(); y++) {
+            final List<Square> columns = rows.get(y).getColumns();
+            for (int x = 0; x < columns.size(); x++) {
+                Square sq = columns.get(x);
+                final SquareType newState = arr[y][x];
+                if (newState != null && newState != sq.getState()) {
+                    sq.setState(newState);
+                }
+            }
         }
         
         if (!emptyHidden) {
@@ -151,25 +163,27 @@
         }
     }
     
-    private static void incrementAround(Mines model, int x, int y) {
-        incrementAt(model, x - 1, y - 1);
-        incrementAt(model, x - 1, y);
-        incrementAt(model, x - 1, y + 1);
+    private static void incrementAround(SquareType[][] arr, int x, int y) {
+        incrementAt(arr, x - 1, y - 1);
+        incrementAt(arr, x - 1, y);
+        incrementAt(arr, x - 1, y + 1);
 
-        incrementAt(model, x + 1, y - 1);
-        incrementAt(model, x + 1, y);
-        incrementAt(model, x + 1, y + 1);
+        incrementAt(arr, x + 1, y - 1);
+        incrementAt(arr, x + 1, y);
+        incrementAt(arr, x + 1, y + 1);
         
-        incrementAt(model, x, y - 1);
-        incrementAt(model, x, y + 1);
+        incrementAt(arr, x, y - 1);
+        incrementAt(arr, x, y + 1);
     }
     
-    private static void incrementAt(Mines model, int x, int y) {
-        if (y >= 0 && y < model.getRows().size()) {
-            Row r = model.getRows().get(y);
-            if (x >= 0 && x < r.getColumns().size()) {
-                Square sq = r.getColumns().get(x);
-                sq.setState(sq.getState().moreBombs());
+    private static void incrementAt(SquareType[][] arr, int x, int y) {
+        if (y >= 0 && y < arr.length) {
+            SquareType[] r = arr[y];
+            if (x >= 0 && x < r.length) {
+                SquareType sq = r[x];
+                if (sq != null) {
+                    r[x] = sq.moreBombsAround();
+                }
             }
         }
     }