diff -r 03bec9dcc860 -r f8f222243d3c minesweeper/src/main/java/org/apidesign/demo/minesweeper/MinesModel.java
--- a/minesweeper/src/main/java/org/apidesign/demo/minesweeper/MinesModel.java	Mon Feb 10 16:50:08 2014 +0100
+++ b/minesweeper/src/main/java/org/apidesign/demo/minesweeper/MinesModel.java	Sun Mar 16 08:30:22 2014 +0100
@@ -111,13 +111,23 @@
     }
     
     @ModelOperation static void init(Mines model, int width, int height, int mines) {
-        List<Row> rows = new ArrayList<Row>(height);
-        for (int y = 0; y < height; y++) {
-            Square[] columns = new Square[width];
-            for (int x = 0; x < width; x++) {
-                columns[x] = new Square(SquareType.UNKNOWN, false);
+        List<Row> rows = model.getRows();
+        if (rows.size() != height || rows.get(0).getColumns().size() != width) {
+            rows = new ArrayList<Row>(height);
+            for (int y = 0; y < height; y++) {
+                Square[] columns = new Square[width];
+                for (int x = 0; x < width; x++) {
+                    columns[x] = new Square(SquareType.UNKNOWN, false);
+                }
+                rows.add(new Row(columns));
             }
-            rows.add(new Row(columns));
+        } else {
+            for (Row row : rows) {
+                for (Square sq : row.getColumns()) {
+                    sq.setState(SquareType.UNKNOWN);
+                    sq.setMine(false);
+                }
+            }
         }
         
         Random r = new Random();
@@ -133,8 +143,10 @@
         }
 
         model.setState(GameState.IN_PROGRESS);
-        model.getRows().clear();
-        model.getRows().addAll(rows);
+        if (rows != model.getRows()) {
+            model.getRows().clear();
+            model.getRows().addAll(rows);
+        }
     }
     
     @ModelOperation static void computeMines(Mines model) {
@@ -233,6 +245,7 @@
                 } else {
                     TOUCH.play();
                     expandKnown(model, data);
+                    model.computeMines();
                 }
             break;
         }
@@ -260,9 +273,18 @@
         }
         final Square sq = columns.get(x);
         if (sq.getState() == SquareType.UNKNOWN) {
-            sq.setState(SquareType.N_0);
-            model.computeMines();
-            if (sq.getState() == SquareType.N_0) {
+            int around = 
+                minesAt(model, x - 1, y - 1) +
+                minesAt(model, x - 1, y) +
+                minesAt(model, x - 1, y + 1) +
+                minesAt(model, x , y - 1) +
+                minesAt(model, x, y + 1) +
+                minesAt(model, x + 1, y - 1) +
+                minesAt(model, x + 1, y) +
+                minesAt(model, x + 1, y + 1);
+            final SquareType t = SquareType.valueOf("N_" + around);
+            sq.setState(t);
+            if (t == SquareType.N_0) {
                 expandKnown(model, x - 1, y - 1);
                 expandKnown(model, x - 1, y);
                 expandKnown(model, x - 1, y + 1);
@@ -274,4 +296,17 @@
             }
         }
     }
+    
+    private static int minesAt(Mines model, int x, int y) {
+        if (y < 0 || y >= model.getRows().size()) {
+            return 0;
+        }
+        final List<Square> columns = model.getRows().get(y).getColumns();
+        if (x < 0 || x >= columns.size()) {
+            return 0;
+        }
+        Square sq = columns.get(x);
+        return sq.isMine() ? 1 : 0;
+    }
+    
 }