diff --git a/stepmania/src/Course.cpp b/stepmania/src/Course.cpp
index 4e4916beeb..e4bc66bbf2 100644
--- a/stepmania/src/Course.cpp
+++ b/stepmania/src/Course.cpp
@@ -256,6 +256,11 @@ void Course::LoadFromCRSFile( CString sPath )
 	m_sMainTitleTranslit = title.TitleTranslit;
 }
 
+void Course::RevertFromDisk()
+{
+	LoadFromCRSFile( m_sPath );
+}
+
 void Course::Init()
 {
 	m_bIsAutogen = false;
@@ -898,9 +903,9 @@ void Course::GetTrails( vector<Trail*> &AddTo, StepsType st ) const
 
 bool Course::HasMods() const
 {
-	for( unsigned i=0; i<m_entries.size(); i++ )
+	FOREACH_CONST( CourseEntry, m_entries, e )
 	{
-		if( !m_entries[i].modifiers.empty() || !m_entries[i].attacks.empty() )
+		if( !e->modifiers.empty() || !e->attacks.empty() )
 			return true;
 	}
 
@@ -909,17 +914,44 @@ bool Course::HasMods() const
 
 bool Course::AllSongsAreFixed() const
 {
-	for( unsigned i=0; i<m_entries.size(); i++ )
+	FOREACH_CONST( CourseEntry, m_entries, e )
 	{
-		if( m_entries[i].type != COURSE_ENTRY_FIXED )
+		if( e->type != COURSE_ENTRY_FIXED )
 			return false;
 	}
 	return true;
 }
 
-void Course::RegenTrails()
+void Course::Invalidate( Song *pStaleSong )
 {
-	ZERO( m_TrailCacheValid );
+	FOREACH_CONST( CourseEntry, m_entries, e )
+	{
+		if( e->pSong == pStaleSong )	// a fixed entry that references the stale Song
+		{
+			RevertFromDisk();
+			return;
+		}
+	}
+
+	// Invalidate any Trails that contain this song.
+	// If we find a Trail that contains this song, then it's part of a 
+	// non-fixed entry.  So, regenerating the Trail will force different
+	// songs to be chosen.
+	FOREACH_StepsType( st )
+		FOREACH_ShownCourseDifficulty( cd )
+			if( m_TrailCacheValid[st][cd] && !m_TrailCacheNull[st][cd] )
+				if( GetTrail( st, cd )->ContainsSong( pStaleSong ) )
+					m_TrailCacheValid[st][cd] = false;
+}
+
+void Course::RegenerateNonFixedTrails()
+{
+	// Only need to regen Trails if the Course has a random entry.
+	// We can create these Trails on demand because we don't 
+	// calculate RadarValues for Trails with one or more non-fixed 
+	// entry.
+	if( !IsFixed() )
+		ZERO( m_TrailCacheValid );
 }
 
 RageColor Course::GetColor() const
diff --git a/stepmania/src/Course.h b/stepmania/src/Course.h
index 6fa2ea816a..574dec8b29 100644
--- a/stepmania/src/Course.h
+++ b/stepmania/src/Course.h
@@ -127,6 +127,7 @@ public:
 	bool IsFixed() const;
 
 	void LoadFromCRSFile( CString sPath );
+	void RevertFromDisk();
 	void Init();
 	void Save();
 	void AutogenEndlessFromGroup( CString sGroupName, Difficulty dc );
@@ -140,8 +141,11 @@ public:
 
 	void UpdateCourseStats( StepsType st );
 
-	/* Call to generate Trails with random entries and if song or notes pointers change. */
-	void RegenTrails();
+	/* Call to regenerate Trails with random entries */
+	void RegenerateNonFixedTrails();
+
+	/* Call when a Song or its Steps are deleted/changed. */
+	void Invalidate( Song *pStaleSong );
 
 private:
 	bool GetTrailUnsorted( StepsType st, CourseDifficulty cd, Trail &trail ) const;
diff --git a/stepmania/src/GameState.cpp b/stepmania/src/GameState.cpp
index e2ba18cc10..1ba10b2ee6 100644
--- a/stepmania/src/GameState.cpp
+++ b/stepmania/src/GameState.cpp
@@ -150,7 +150,7 @@ void GameState::Reset()
 
 	/* We may have cached trails from before everything was loaded (eg. from before
 	 * SongManager::UpdateBest could be called).  Erase the cache. */
-	SONGMAN->FlushCaches();
+	SONGMAN->RegenerateNonFixedCourses();
 
 	g_vPlayedStageStats.clear();
 
diff --git a/stepmania/src/ScreenGameplay.cpp b/stepmania/src/ScreenGameplay.cpp
index dc5f356e1e..9365a479a2 100644
--- a/stepmania/src/ScreenGameplay.cpp
+++ b/stepmania/src/ScreenGameplay.cpp
@@ -1815,15 +1815,14 @@ void SaveChanges( void* papSongsQueue )
 void RevertChanges( void* papSongsQueue )
 {
 	vector<Song*>& apSongsQueue = *(vector<Song*>*)papSongsQueue;
-	for( unsigned i=0; i<apSongsQueue.size(); i++ )
-		apSongsQueue[i]->RevertFromDisk();
+	FOREACH( Song*, apSongsQueue, pSong )
+	{
+		(*pSong)->RevertFromDisk();
 
-	// We need to regen any Courses that have any of the songs we just reloaded.
-	// Regen all Courses for now.
-	vector<Course*> vpAllCourses;
-	SONGMAN->GetAllCourses( vpAllCourses, true );
-	FOREACH( Course*, vpAllCourses, pCourse )
-		(*pCourse)->RegenTrails();
+		// We need to regen any Courses that have any of the songs we just reloaded.
+		// Regen all Courses for now.
+		SONGMAN->Invalidate( *pSong );
+	}
 }
 
 void ScreenGameplay::ShowSavePrompt( ScreenMessage SM_SendWhenDone )
diff --git a/stepmania/src/Song.cpp b/stepmania/src/Song.cpp
index 224af9ee41..9320fb4db2 100644
--- a/stepmania/src/Song.cpp
+++ b/stepmania/src/Song.cpp
@@ -86,7 +86,9 @@ Song::~Song()
 	m_vpSteps.clear();
 
 	/* We deleted some Steps*; clear stuff that used it. */
-	SONGMAN->FlushCaches();
+	/* Don't make Song depend on SongManager.  It's leading to some 
+	 * confusing limitation on what can be done in SONGMAN->FlushCaches(). */
+	SONGMAN->Invalidate( this );
 }
 
 /* Reset to an empty song. */
@@ -103,7 +105,7 @@ void Song::Reset()
 
 	/* Courses cache Notes* pointers.  On the off chance that this isn't the last
 	 * thing this screen does, clear that cache. */
-	SONGMAN->FlushCaches();
+	SONGMAN->Invalidate( this );
 }
 
 
@@ -348,7 +350,7 @@ void Song::RevertFromDisk( bool bAllowNotesLoss )
 		}
 	}
 
-	StepsID::FlushCache();
+	StepsID::Invalidate( this );
 }
 
 
diff --git a/stepmania/src/SongManager.cpp b/stepmania/src/SongManager.cpp
index cfaa7f2403..4055b1a196 100644
--- a/stepmania/src/SongManager.cpp
+++ b/stepmania/src/SongManager.cpp
@@ -28,6 +28,7 @@
 #include "RageFileManager.h"
 #include "UnlockSystem.h"
 #include "CatalogXml.h"
+#include "Foreach.h"
 
 SongManager*	SONGMAN = NULL;	// global and accessable from anywhere in our program
 
@@ -78,8 +79,8 @@ SongManager::SongManager()
 
 SongManager::~SongManager()
 {
-	FreeSongs();
 	FreeCourses();
+	FreeSongs();
 }
 
 void SongManager::InitAll( LoadingWindow *ld )
@@ -665,13 +666,19 @@ void SongManager::Cleanup()
 /* Flush all Song*, Steps* and Course* caches.  This is called on reload, and when
  * any of those are removed or changed.  This doesn't touch GAMESTATE and StageStats
  * pointers, which are updated explicitly in Song::RevertFromDisk. */
-void SongManager::FlushCaches()
+void SongManager::Invalidate( Song *pStaleSong )
 {
 	/* Erase cached course info. */
-	for( unsigned i=0; i < m_pCourses.size(); i++ )
-		m_pCourses[i]->RegenTrails();
+	FOREACH_CONST( Course*, m_pCourses, c )
+		(*c)->Invalidate( pStaleSong );
 
-	StepsID::FlushCache();
+	StepsID::Invalidate( pStaleSong );
+}
+
+void SongManager::RegenerateNonFixedCourses()
+{
+	for( unsigned i=0; i < m_pCourses.size(); i++ )
+		m_pCourses[i]->RegenerateNonFixedTrails();
 }
 
 void SongManager::SetPreferences()
diff --git a/stepmania/src/SongManager.h b/stepmania/src/SongManager.h
index c5934c7966..61ea8fb812 100644
--- a/stepmania/src/SongManager.h
+++ b/stepmania/src/SongManager.h
@@ -25,7 +25,10 @@ public:
 	void InitSongsFromDisk( LoadingWindow *ld );
 	void FreeSongs();
 	void Cleanup();
-	void FlushCaches();
+
+	void Invalidate( Song *pStaleSong );
+
+	void RegenerateNonFixedCourses();
 	void SetPreferences();
 
 	void LoadAllFromProfiles();	// song, edits
diff --git a/stepmania/src/StepsUtil.cpp b/stepmania/src/StepsUtil.cpp
index c18bda9d08..768f64b4f6 100644
--- a/stepmania/src/StepsUtil.cpp
+++ b/stepmania/src/StepsUtil.cpp
@@ -184,8 +184,9 @@ XNode* StepsID::CreateNode() const
 }
 
 
-void StepsID::FlushCache()
+void StepsID::Invalidate( Song *pStaleSong )
 {
+	// FIXME: Only flush entries with the stale song
 	g_StepsIDCache.clear();
 }
 
diff --git a/stepmania/src/StepsUtil.h b/stepmania/src/StepsUtil.h
index 2546c38fba..39a77b6af4 100644
--- a/stepmania/src/StepsUtil.h
+++ b/stepmania/src/StepsUtil.h
@@ -39,7 +39,7 @@ public:
 	void LoadFromNode( const XNode* pNode );
 	CString ToString() const;
 	bool IsValid() const;
-	static void FlushCache();
+	static void Invalidate( Song *pStaleSong );
 };
 
 #endif
diff --git a/stepmania/src/StyleUtil.h b/stepmania/src/StyleUtil.h
index a6016d37c5..1e129cdb84 100644
--- a/stepmania/src/StyleUtil.h
+++ b/stepmania/src/StyleUtil.h
@@ -20,7 +20,7 @@ public:
 	XNode* CreateNode() const;
 	void LoadFromNode( const XNode* pNode );
 	bool IsValid() const;
-	static void FlushCache();
+	static void FlushCache( Song* pStaleSong );
 };
 
 #endif
diff --git a/stepmania/src/Trail.cpp b/stepmania/src/Trail.cpp
index a83512cb1e..6a418e417d 100644
--- a/stepmania/src/Trail.cpp
+++ b/stepmania/src/Trail.cpp
@@ -51,7 +51,14 @@ bool TrailEntry::ContainsTransformOrTurn() const
 
 RadarValues Trail::GetRadarValues() const
 {
-	if( m_bRadarValuesCached )
+	if( IsMystery() )
+	{
+		// Don't calculate RadarValues for a non-fixed Course.  They values are 
+		// worthless because they'll change every time this Trail is 
+		// regenerated.
+		return RadarValues();
+	}
+	else if( m_bRadarValuesCached )
 	{
 		return m_CachedRadarValues;
 	}
@@ -152,6 +159,26 @@ void Trail::GetDisplayBpms( DisplayBpms &AddTo )
 	}
 }
 
+bool Trail::IsMystery() const
+{
+	FOREACH_CONST( TrailEntry, m_vEntries, e )
+	{
+		if( e->bMystery )
+			return true;
+	}
+	return false;
+}
+
+bool Trail::ContainsSong( Song* pSong ) const
+{
+	FOREACH_CONST( TrailEntry, m_vEntries, e )
+	{
+		if( e->pSong == pSong )
+			return true;
+	}
+	return false;
+}
+
 /*
  * (c) 2001-2004 Chris Danford, Glenn Maynard
  * All rights reserved.
diff --git a/stepmania/src/Trail.h b/stepmania/src/Trail.h
index 82a1309d2d..8e76ca84c5 100644
--- a/stepmania/src/Trail.h
+++ b/stepmania/src/Trail.h
@@ -66,6 +66,8 @@ public:
 	int GetTotalMeter() const;
 	float GetLengthSeconds() const;
 	void GetDisplayBpms( DisplayBpms &AddTo );
+	bool IsMystery() const;
+	bool ContainsSong( Song* pSong ) const;
 };
 
 #endif
diff --git a/stepmania/src/TrailUtil.h b/stepmania/src/TrailUtil.h
index cd5fd09e40..5131a1a34e 100644
--- a/stepmania/src/TrailUtil.h
+++ b/stepmania/src/TrailUtil.h
@@ -3,6 +3,7 @@
 
 #include "GameConstantsAndTypes.h"
 
+class Song;
 class Trail;
 class Course;
 struct XNode;
@@ -24,7 +25,7 @@ public:
 	void LoadFromNode( const XNode* pNode );
 	CString ToString() const;
 	bool IsValid() const;
-	static void FlushCache();
+	static void Invalidate( Song* pStaleSong );
 };
 
 #endif