diff --git a/app/src/main/AndroidManifest.xml b/app/src/main/AndroidManifest.xml
index d80ae9f..f26ab73 100644
--- a/app/src/main/AndroidManifest.xml
+++ b/app/src/main/AndroidManifest.xml
@@ -1,6 +1,6 @@
 <?xml version="1.0" encoding="utf-8"?>
 <manifest xmlns:android="http://schemas.android.com/apk/res/android"
-      package="org.ab.x48" android:installLocation="auto" android:versionCode="76" android:versionName="1.76">
+      package="org.ab.x48" android:installLocation="auto" android:versionCode="77" android:versionName="1.77">
     <application android:icon="@drawable/icon" android:label="@string/app_name">
         <activity android:name=".X48"
                   android:label="@string/app_name"
diff --git a/app/src/main/java/org/ab/x48/HPView.java b/app/src/main/java/org/ab/x48/HPView.java
index eb283a0..f5dbec3 100644
--- a/app/src/main/java/org/ab/x48/HPView.java
+++ b/app/src/main/java/org/ab/x48/HPView.java
@@ -34,6 +34,7 @@ import android.view.KeyEvent;
 import android.view.MotionEvent;
 import android.view.SurfaceHolder;
 import android.view.SurfaceView;
+import android.view.View;
 
 public class HPView extends SurfaceView implements SurfaceHolder.Callback {
 
@@ -42,6 +43,7 @@ public class HPView extends SurfaceView implements SurfaceHolder.Callback {
 	private Bitmap mainScreen;
 	private SurfaceHolder mSurfaceHolder;
 	private boolean surfaceValid;
+	private int visibility = VISIBLE;
 	private Bitmap  annImages [];
     private Bitmap  menuIcon;
 	boolean ann [];
@@ -945,6 +947,12 @@ public class HPView extends SurfaceView implements SurfaceHolder.Callback {
 		//Log.i("x48", "data: " + data.length);
 	}
 
+	@Override
+	protected void onVisibilityChanged(View changedView, int visibility) {
+		super.onVisibilityChanged(changedView, visibility);
+		this.visibility = visibility;
+	}
+
 	@Override
 	public boolean onTouchEvent(MotionEvent event) {
 		synchronized (mSurfaceHolder) {
@@ -1072,7 +1080,9 @@ public class HPView extends SurfaceView implements SurfaceHolder.Callback {
 		else
 			currentOrientation = Configuration.ORIENTATION_LANDSCAPE;
 		//initGraphicsElements();
-		backBuffer = null;
+		synchronized (mSurfaceHolder) {
+			backBuffer = null;
+		}
 		x48.flipScreen();
 	}
 	
@@ -1116,7 +1126,7 @@ public class HPView extends SurfaceView implements SurfaceHolder.Callback {
 	}
 
 	public void refresh() {
-		if (surfaceValid) {
+		if (surfaceValid && visibility == VISIBLE) {
 			if (needFlip || x48.fillScreenData(buf, ann) == 1) {
 				needFlip = false;
 				refreshMainScreen(buf);