diff --git a/src/commands/SelectCommand.cpp b/src/commands/SelectCommand.cpp
index c44a49c20..4a4144c6d 100644
--- a/src/commands/SelectCommand.cpp
+++ b/src/commands/SelectCommand.cpp
@@ -207,6 +207,10 @@ void SelectTracksCommand::PopulateOrExchange(ShuttleGui & S)
 
 bool SelectTracksCommand::Apply(const CommandContext &context)
 {
+
+   // Count selection as a do-nothing effect.
+   // Used to invalidate cached selection and tracks.
+   Effect::IncEffectCounter();
    int index = 0;
    TrackList *tracks = context.GetProject()->GetTracks();
 
diff --git a/src/effects/Effect.cpp b/src/effects/Effect.cpp
index d0af0ac52..974a1c9ba 100644
--- a/src/effects/Effect.cpp
+++ b/src/effects/Effect.cpp
@@ -70,6 +70,9 @@ greater use in future.
 
 #include <unordered_map>
 
+// Effect application counter
+int Effect::nEffectsDone=0;
+
 static const int kDummyID = 20000;
 static const int kSaveAsID = 20001;
 static const int kImportID = 20002;
@@ -1074,8 +1077,9 @@ bool Effect::SetAutomationParameters(const wxString & parms)
             preset
          )
       );
-
-      return false;
+      // We are using defualt settings and we still wish to continue.
+      return true;
+      //return false;
    }
 
    if (!mUIDialog)
@@ -1246,7 +1250,7 @@ bool Effect::DoEffect(wxWindow *parent,
       returnVal = Process();
    }
 
-   if (returnVal)
+   if (returnVal && (mT1 >= mT0 ))
    {
       selectedRegion->setTimes(mT0, mT1);
    }
@@ -2246,6 +2250,7 @@ void Effect::ReplaceProcessedTracks(const bool bGoodResult)
    // The output list is no longer needed
    mOutputTracks.reset();
    mOutputTracksType = Track::None;
+   nEffectsDone++;
 }
 
 void Effect::CountWaveTracks()
diff --git a/src/effects/Effect.h b/src/effects/Effect.h
index de3ddbd02..19b051b9c 100644
--- a/src/effects/Effect.h
+++ b/src/effects/Effect.h
@@ -270,6 +270,8 @@ class AUDACITY_DLL_API Effect /* not final */ : public wxEvtHandler,
                   long style = DefaultMessageBoxStyle,
                   const wxString& titleStr = wxString{});
 
+   static void IncEffectCounter(){ nEffectsDone++;};
+
 //
 // protected virtual methods
 //
@@ -341,7 +343,6 @@ protected:
    bool TrackGroupProgress(int whichGroup, double frac, const wxString & = wxEmptyString);
 
    int GetNumWaveTracks() { return mNumTracks; }
-
    int GetNumWaveGroups() { return mNumGroups; }
 
    // Calculates the start time and selection length in samples
@@ -370,6 +371,9 @@ protected:
    void CopyInputTracks(); // trackType = Track::Wave
    void CopyInputTracks(int trackType);
 
+   // A global counter of all the successful Effect invocations.
+   static int nEffectsDone;
+
    // For the use of analyzers, which don't need to make output wave tracks,
    // but may need to add label tracks.
    class AddedAnalysisTrack {
diff --git a/src/effects/nyquist/Nyquist.cpp b/src/effects/nyquist/Nyquist.cpp
index 851f8effb..fc7740254 100644
--- a/src/effects/nyquist/Nyquist.cpp
+++ b/src/effects/nyquist/Nyquist.cpp
@@ -75,6 +75,8 @@ effects from this one class.
 
 #include "../../Experimental.h"
 
+int NyquistEffect::mReentryCount = 0;
+
 enum
 {
    ID_Editor = 10000,
@@ -584,10 +586,21 @@ static void RegisterFunctions();
 
 bool NyquistEffect::Process()
 {
+   // Check for reentrant Nyquist commands.
+   // I'm choosing to mark skipped Nyquist commands as successful even though
+   // they are skipped.  The reason is that when Nyquist calls out to a chain,
+   // and that chain contains Nyquist,  it will be clearer if the chain completes 
+   // skipping Nyquist, rather than doing nothing at all.
+   if( mReentryCount > 0 )
+      return true;
+
+   // Restore the reentry counter (to zero) when we exit.
+   auto cleanup = valueRestorer( mReentryCount);
+   mReentryCount++;
    RegisterFunctions();
 
    bool success = true;
-
+   int nEffectsSoFar = nEffectsDone;
    mProjectChanged = false;
    EffectManager & em = EffectManager::Get();
    em.SetSkipStateFlag(false);
@@ -894,7 +907,13 @@ finish:
       dlog.ShowModal();
    }
 
-   ReplaceProcessedTracks(success);
+   // Has rug been pulled from under us by some effect done within Nyquist??
+   if( nEffectsSoFar == nEffectsDone )
+      ReplaceProcessedTracks(success);
+   else{
+      ReplaceProcessedTracks(false); // Do not use the results.
+      mT1 = mT0 - 1.0;// And don't use the times either, in resetting the selection  (make them bogus).
+   }
 
    if (!mProjectChanged)
       em.SetSkipStateFlag(true);
diff --git a/src/effects/nyquist/Nyquist.h b/src/effects/nyquist/Nyquist.h
index 103d6fb7b..97869dd9f 100644
--- a/src/effects/nyquist/Nyquist.h
+++ b/src/effects/nyquist/Nyquist.h
@@ -129,6 +129,7 @@ public:
    void Stop();
 
 private:
+   static int mReentryCount;
    // NyquistEffect implementation
 
    bool ProcessOne();