AntennaRelay: Log when encountering a null vessel in FlightGlobals.
AntennaRelay: Log when encountering a null vessel in FlightGlobals.

--- a/AntennaRelay.cs
+++ b/AntennaRelay.cs
@@ -221,6 +221,7 @@
 				
 				if (potentialVessel == null)
 				{
+					Tools.PostErrorMessage("{0}: Skipping vessel at index {1} because it is null.", this, vIdx);
 					log.AppendFormat("\n\tSkipping vessel at index {0} because it is null.", vIdx);
 					log.Print();
 					return;

--- a/ProtoAntennaRelay.cs
+++ b/ProtoAntennaRelay.cs
@@ -48,7 +48,11 @@
 		{
 			get
 			{
-				if (this.protoPart != null && this.protoPart.pVesselRef != null)
+				if (
+					this.protoPart != null &&
+					this.protoPart.pVesselRef != null &&
+					this.protoPart.pVesselRef.vesselRef != null
+				)
 				{
 					return this.protoPart.pVesselRef.vesselRef;
 				}

--- a/RelayDatabase.cs
+++ b/RelayDatabase.cs
@@ -72,9 +72,6 @@
 		// Vessel.id-keyed hash table of part counts, used for caching
 		private Dictionary<Guid, int> vesselPartCountTable;
 
-		// Vessel.id-keyed hash table of booleans to track what vessels have been checked so far this time.
-		public Dictionary<Guid, bool> CheckedVesselsTable;
-
 		private int cacheHits;
 		private int cacheMisses;
 
@@ -117,9 +114,16 @@
 		// Remove a vessel from the cache, if it exists.
 		public void DirtyVessel(Vessel vessel)
 		{
+			#if DEBUG
+			Tools.PostDebugMessage("RelayDatabase: Dirtying cache for vessel {0} in frame {1}",
+				vessel, new System.Diagnostics.StackTrace().ToString());
+			#else
+			Tools.PostLogMessage("RelayDatabase: Dirtying cache for vessel {0}", vessel.vesselName);
+			#endif
+
 			this.relayDatabase.Remove(vessel.id);
 			this.vesselPartCountTable.Remove(vessel.id);
-			this.relayDatabase.Remove(vessel.id);
+			this.bestRelayTable.Remove(vessel.id);
 		}
 
 		// Returns true if both the relayDatabase and the vesselPartCountDB contain the vessel id.
@@ -228,11 +232,33 @@
 		// Runs when the player requests a scene change, such as when changing vessels or leaving flight.
 		private void onSceneChange(GameScenes scene)
 		{
-			// If the active vessel is a real thing...
-			if (FlightGlobals.ActiveVessel != null)
-			{
-				// ... dirty its cache
-				this.onVesselEvent(FlightGlobals.ActiveVessel);
+			Tools.PostDebugMessage(
+				"RelayDatabase: caught onSceneChangeRequested in scene {0} to scene {1}.  ActiveVessel is {2}",
+				HighLogic.LoadedScene,
+				scene,
+				FlightGlobals.ActiveVessel == null ? "null" : FlightGlobals.ActiveVessel.vesselName
+			);
+
+			if (scene == GameScenes.FLIGHT)
+			{
+				if (scene == HighLogic.LoadedScene)
+				{
+					if (FlightGlobals.ActiveVessel != null)
+					{
+						Tools.PostDebugMessage("RelayDatabase: onSceneChange clearing {0} from cache.",
+							FlightGlobals.ActiveVessel.vesselName);
+
+						this.onVesselEvent(FlightGlobals.ActiveVessel);
+					}
+				}
+				else
+				{
+					Tools.PostLogMessage("RelayDatabase: onSceneChange clearing entire cache.");
+
+					this.relayDatabase.Clear();
+					this.bestRelayTable.Clear();
+					this.vesselPartCountTable.Clear();
+				}
 			}
 		}
 
@@ -394,7 +420,6 @@
 			this.relayDatabase = new Dictionary<Guid, List<IAntennaRelay>>();
 			this.bestRelayTable = new Dictionary<Guid, IAntennaRelay>();
 			this.vesselPartCountTable = new Dictionary<Guid, int>();
-			this.CheckedVesselsTable = new Dictionary<Guid, bool>();
 
 			this.cacheHits = 0;
 			this.cacheMisses = 0;