diff --git a/core/src/net/sf/openrocket/motor/ThrustCurveMotor.java b/core/src/net/sf/openrocket/motor/ThrustCurveMotor.java
index 904b87053..51f78e511 100644
--- a/core/src/net/sf/openrocket/motor/ThrustCurveMotor.java
+++ b/core/src/net/sf/openrocket/motor/ThrustCurveMotor.java
@@ -338,11 +338,11 @@ public class ThrustCurveMotor implements Motor, Comparable<ThrustCurveMotor>, Se
 		
 		int timeIndex = 0;
 		
-		while( timeIndex < time.length-2 && startTime > time[timeIndex+1] ) {
+		while( timeIndex < time.length-1 && startTime > time[timeIndex+1] ) {
 			timeIndex++;
 		}
 		
-		if ( timeIndex == time.length ) {
+		if ( timeIndex == time.length-1 ) {
 			return 0.0;
 		}
 		
diff --git a/core/src/net/sf/openrocket/rocketcomponent/FlightConfiguration.java b/core/src/net/sf/openrocket/rocketcomponent/FlightConfiguration.java
index 2ec435327..70f645ab1 100644
--- a/core/src/net/sf/openrocket/rocketcomponent/FlightConfiguration.java
+++ b/core/src/net/sf/openrocket/rocketcomponent/FlightConfiguration.java
@@ -63,6 +63,7 @@ public class FlightConfiguration implements FlightConfigurableParameter<FlightCo
 	/* Cached data */
 	final protected HashMap<Integer, StageFlags> stages = new HashMap<Integer, StageFlags>();
 	final protected HashMap<MotorConfigurationId, MotorConfiguration> motors = new HashMap<MotorConfigurationId, MotorConfiguration>();
+	final private Collection<MotorConfiguration> activeMotors = new ArrayList<MotorConfiguration>();
 	
 	private int boundsModID = -1;
 	private BoundingBox cachedBounds = new BoundingBox();
@@ -109,23 +110,23 @@ public class FlightConfiguration implements FlightConfigurableParameter<FlightCo
 	
 	public void clearAllStages() {
 		this._setAllStages(false);
-		this.updateMotors();
 	}
 	
 	public void setAllStages() {
 		this._setAllStages(true);
-		this.updateMotors();
 	}
 
 	private void _setAllStages(final boolean _active) {
 		for (StageFlags cur : stages.values()) {
 			cur.active = _active;
 		}
+		updateMotors();
 	}
 
 	public void copyStages(FlightConfiguration other) {
 		for (StageFlags cur : other.stages.values())
 			stages.put(cur.stageNumber, new StageFlags(cur.stageNumber, cur.active));
+		updateMotors();
 	}
 	
 	/** 
@@ -135,6 +136,7 @@ public class FlightConfiguration implements FlightConfigurableParameter<FlightCo
 	 */
 	public void clearStage(final int stageNumber) {
 		_setStageActive( stageNumber, false );
+		updateMotors();
 	}
 	
 	/**
@@ -196,7 +198,7 @@ public class FlightConfiguration implements FlightConfigurableParameter<FlightCo
 			flags.active = !flags.active;
 			return;
 		}
-		this.updateMotors();
+		updateMotors();
 		log.error("error: attempt to retrieve via a bad stage number: " + stageNumber);
 	}
 
@@ -498,18 +500,12 @@ public class FlightConfiguration implements FlightConfigurableParameter<FlightCo
 	}
 	
 	public Collection<MotorConfiguration> getActiveMotors() {
-		Collection<MotorConfiguration> activeMotors = new ArrayList<MotorConfiguration>();
-		for( MotorConfiguration config : this.motors.values() ){
-			if( isComponentActive( config.getMount() )){
-				activeMotors.add( config );
-			}
-		}
 		
 		return activeMotors;
 	}
 
 	private void updateMotors() {
-		this.motors.clear();
+		motors.clear();
 		
 		for ( RocketComponent comp : getActiveComponents() ){
 			if (( comp instanceof MotorMount )&&( ((MotorMount)comp).isMotorMount())){
@@ -519,10 +515,16 @@ public class FlightConfiguration implements FlightConfigurableParameter<FlightCo
 					continue;
 				}
 				
-				this.motors.put( motorConfig.getMID(), motorConfig);
+				motors.put( motorConfig.getMID(), motorConfig);
 			}
 		}
 		
+		activeMotors.clear();
+		for( MotorConfiguration config : motors.values() ){
+			if( isComponentActive( config.getMount() )){
+				activeMotors.add( config );
+			}
+		}
 	}
 
 	@Override
diff --git a/core/src/net/sf/openrocket/simulation/AbstractSimulationStepper.java b/core/src/net/sf/openrocket/simulation/AbstractSimulationStepper.java
index 3d753d547..e247da7f4 100644
--- a/core/src/net/sf/openrocket/simulation/AbstractSimulationStepper.java
+++ b/core/src/net/sf/openrocket/simulation/AbstractSimulationStepper.java
@@ -181,7 +181,7 @@ public abstract class AbstractSimulationStepper implements SimulationStepper {
 		
 		thrust = 0;
 		final double currentTime = status.getSimulationTime() + timestep;
-		Collection<MotorClusterState> activeMotorList = status.getMotors();
+		Collection<MotorClusterState> activeMotorList = status.getActiveMotors();
 		for (MotorClusterState currentMotorState : activeMotorList ) {
 			thrust += currentMotorState.getAverageThrust( status.getSimulationTime(), currentTime );
 			//thrust += currentMotorState.getThrust( currentTime );