diff --git a/android/src/net/sf/openrocket/android/CurrentRocket.java b/android/src/net/sf/openrocket/android/CurrentRocket.java
index aafbb0631..7546808d5 100644
--- a/android/src/net/sf/openrocket/android/CurrentRocket.java
+++ b/android/src/net/sf/openrocket/android/CurrentRocket.java
@@ -2,6 +2,8 @@ package net.sf.openrocket.android;
 
 import java.io.File;
 import java.io.IOException;
+import java.util.HashSet;
+import java.util.Set;
 
 import net.sf.openrocket.aerodynamics.WarningSet;
 import net.sf.openrocket.document.OpenRocketDocument;
@@ -21,6 +23,7 @@ public class CurrentRocket {
 	private RocketChangedEventHandler handler;
 	
 	private boolean isModified = false;
+	private Set<Integer> runningSims = new HashSet<Integer>();
 	
 	public void setHandler( RocketChangedEventHandler handler ) {
 		this.handler = handler;
@@ -34,12 +37,35 @@ public class CurrentRocket {
 	}
 
 	public void notifySimsChanged() {
-		isModified = true;
+		synchronized ( this ) {
+			isModified = true;
+		}
 		if ( handler != null ) {
 			handler.simsChangedMessage();
 		}
 	}
 
+	public void notifySimComplete() {
+		synchronized ( this ) {
+			isModified = true;
+		}
+		if ( handler != null ) {
+			handler.simCompleteMessage();
+		}
+	}
+
+	public synchronized void lockSimulation( int simulationId ) {
+		runningSims.add(simulationId);
+	}
+	
+	public synchronized void unlockSimulation( int simulationId ) {
+		runningSims.remove(simulationId);
+	}
+	
+	public synchronized Set<Integer> lockedSimulations() {
+		return new HashSet<Integer>(runningSims);
+	}
+	
 	public void addNewSimulation() {
 		Rocket rocket = rocketDocument.getRocket();
 		// FIXME - hopefully the change to the Simulation object will be reverted soon.
@@ -55,7 +81,9 @@ public class CurrentRocket {
 	}
 	
 	public String addNewMotorConfig() {
-		isModified = true;
+		synchronized ( this ) {
+			isModified = true;
+		}
 		String configId = rocketDocument.getRocket().newMotorConfigurationID();
 		if ( handler != null ) {
 			handler.configsChangedMessage();
@@ -67,7 +95,9 @@ public class CurrentRocket {
 	 */
 	public void setRocketDocument(OpenRocketDocument rocketDocument) {
 		this.rocketDocument = rocketDocument;
-		isModified = false;
+		synchronized ( this ) {
+			isModified = false;
+		}
 	}
 
 	public WarningSet getWarnings() {
@@ -90,6 +120,10 @@ public class CurrentRocket {
 		return this.isModified;
 	}
 	
+	public boolean canSave() {
+		return this.isModified && this.runningSims.isEmpty();
+	}
+	
 	public void saveOpenRocketDocument() throws IOException {
 		
 		// Translate the fileUri if it happens to be a .rkt file.
diff --git a/android/src/net/sf/openrocket/android/RocketChangedEventHandler.java b/android/src/net/sf/openrocket/android/RocketChangedEventHandler.java
index a7d5db654..06668fa37 100644
--- a/android/src/net/sf/openrocket/android/RocketChangedEventHandler.java
+++ b/android/src/net/sf/openrocket/android/RocketChangedEventHandler.java
@@ -23,7 +23,13 @@ public abstract class RocketChangedEventHandler extends Handler {
 
 	public static final int MOTOR_CONFIGS_CHANGED = 1;
 	public static final int SIMS_CHANGED = 2;
+	public static final int SIM_COMPLETE = 3;
 
+	public void simCompleteMessage() {
+		Message m = this.obtainMessage(SIM_COMPLETE);
+		this.sendMessage(m);
+	}
+	
 	public void simsChangedMessage() {
 		Message m = this.obtainMessage(SIMS_CHANGED);
 		this.sendMessage(m);
@@ -44,11 +50,16 @@ public abstract class RocketChangedEventHandler extends Handler {
 		case MOTOR_CONFIGS_CHANGED:
 			doMotorConfigsChanged();
 			break;
+		case SIM_COMPLETE:
+			doSimComplete();
+			break;
 		default:
 			super.handleMessage(msg);
 		}
 	}
 
+	protected abstract void doSimComplete();
+	
 	protected abstract void doSimsChanged();
 	
 	protected abstract void doMotorConfigsChanged();
diff --git a/android/src/net/sf/openrocket/android/rocket/OpenRocketViewer.java b/android/src/net/sf/openrocket/android/rocket/OpenRocketViewer.java
index 2304aa9a6..5274912e6 100644
--- a/android/src/net/sf/openrocket/android/rocket/OpenRocketViewer.java
+++ b/android/src/net/sf/openrocket/android/rocket/OpenRocketViewer.java
@@ -111,7 +111,7 @@ implements Simulations.OnSimulationSelectedListener, OpenRocketSaverFragment.OnO
 		MenuInflater inflater = getSupportMenuInflater();
 		inflater.inflate(R.menu.rocket_viewer_option_menu, menu);
 		MenuItem saveAction = menu.findItem(R.id.menu_save);
-		if ( CurrentRocketHolder.getCurrentRocket().isModified() ) {
+		if ( CurrentRocketHolder.getCurrentRocket().canSave() ) {
 			saveAction.setVisible(true);
 			saveAction.setShowAsAction( MenuItem.SHOW_AS_ACTION_ALWAYS );
 		} else {
@@ -207,7 +207,7 @@ implements Simulations.OnSimulationSelectedListener, OpenRocketSaverFragment.OnO
 
 	private void saveRocketDocument() {
 		getSupportFragmentManager().beginTransaction()
-		.add( OpenRocketSaverFragment.newInstance(false), "saver")
+		.add( OpenRocketSaverFragment.newInstance(true), "saver")
 		.commitAllowingStateLoss();
 	}
 
@@ -223,11 +223,16 @@ implements Simulations.OnSimulationSelectedListener, OpenRocketSaverFragment.OnO
 	private class RocketChangedEventHandler extends net.sf.openrocket.android.RocketChangedEventHandler {
 
 		@Override
-		protected void doSimsChanged() {
+		protected void doSimComplete() {
 			if ( autoSaveEnabled ) {
 				Toast.makeText(OpenRocketViewer.this, R.string.autoSaveMessage, Toast.LENGTH_SHORT).show();
 				OpenRocketViewer.this.saveRocketDocument();
 			}
+			doSimsChanged();
+		}
+
+		@Override
+		protected void doSimsChanged() {
 			invalidateOptionsMenu();
 			Simulations sims = (Simulations) viewPagerAdapter.getFragmentAtPos(SIMS_POS);
 			if ( sims != null ) {
diff --git a/android/src/net/sf/openrocket/android/simservice/SimulationService.java b/android/src/net/sf/openrocket/android/simservice/SimulationService.java
index dad46292f..65d9d8171 100644
--- a/android/src/net/sf/openrocket/android/simservice/SimulationService.java
+++ b/android/src/net/sf/openrocket/android/simservice/SimulationService.java
@@ -39,6 +39,7 @@ public class SimulationService extends IntentService {
 			Simulation sim = CurrentRocketHolder.getCurrentRocket().getRocketDocument().getSimulation(t.simulationId);
 			AndroidLogWrapper.d(SimulationService.class, "simulating " + t.simulationId );
 			sim.simulate();
+			CurrentRocketHolder.getCurrentRocket().unlockSimulation(t.simulationId);
 			CurrentRocketHolder.getCurrentRocket().notifySimsChanged();
 		}
 		catch (SimulationException simex) {