diff --git a/src/common/interfaces.h b/src/common/interfaces.h
index df7bc0f78..debcc13f0 100644
--- a/src/common/interfaces.h
+++ b/src/common/interfaces.h
@@ -538,12 +538,20 @@ public:
 	// Called when the user press the second time the button 
 	virtual void EndEdit(MeshModel &/*m*/, GLArea * /*parent*/){}
     
+
+	// There are two classes of editing tools, the one that works on a single layer at a time
+	// and the ones that works on all layers and have to manage in a correct way the action of changing the current layer.
+	// For the edit tools that works ona single layer changing the layer means the restart of the edit tool.
+	virtual bool isSingleMeshEdit() const { return true; }
+
 	// Called when the user changes the selected layer
 	//by default it calls end edit with the layer that was selected and start with the new layer that is
 	//selected.  This ensures that plugins who dont support layers do not get sent pointers to meshes
-	//they are not expecting
+	//they are not expecting.
+	// If your editing plugins is not singleMesh you MUST reimplement this to correctly handle the change of layer.
 	virtual void LayerChanged(MeshDocument &md, MeshModel &oldMeshModel, GLArea *parent)
 	{
+		assert(this->isSingleMeshEdit());
 		EndEdit(oldMeshModel, parent);
 		StartEdit(md, parent);
 	}
@@ -554,8 +562,7 @@ public:
 	virtual void mousePressEvent  (QMouseEvent *event, MeshModel &/*m*/, GLArea * )=0;
 	virtual void mouseMoveEvent   (QMouseEvent *event, MeshModel &/*m*/, GLArea * )=0;
 	virtual void mouseReleaseEvent(QMouseEvent *event, MeshModel &/*m*/, GLArea * )=0;
-	//virtual void wheelEvent     (QWheelEvent*e, MeshModel &/*m*/, GLArea * );
-  virtual void keyReleaseEvent  (QKeyEvent *, MeshModel &/*m*/, GLArea *){}
+	  virtual void keyReleaseEvent  (QKeyEvent *, MeshModel &/*m*/, GLArea *){}
   virtual void keyPressEvent    (QKeyEvent *, MeshModel &/*m*/, GLArea *){}
   virtual void wheelEvent(QWheelEvent*, MeshModel &/*m*/, GLArea * ){}
   virtual void tabletEvent(QTabletEvent * e, MeshModel &/*m*/, GLArea *){e->ignore();}
diff --git a/src/meshlab/glarea.cpp b/src/meshlab/glarea.cpp
index 8c0822214..7f9e03f60 100644
--- a/src/meshlab/glarea.cpp
+++ b/src/meshlab/glarea.cpp
@@ -648,7 +648,10 @@ void GLArea::updateLayer()
     //if we have an edit tool open, notify it that the current layer has changed
 	if(iEdit)
 	{
-		assert(lastModelEdited);  //if there is an editor last model edited should always be set when start edit is called
+	if(iEdit->isSingleMeshEdit())
+	  assert(lastModelEdited);  // if there is an editor that works on a single mesh
+								// last model edited should always be set when start edit is called
+
     iEdit->LayerChanged(*this->md(), *lastModelEdited, this);
 
 		//now update the last model edited
@@ -686,7 +689,9 @@ void GLArea::setCurrentEditAction(QAction *editAction)
   else
   {
     log->Logf(GLLogStream::SYSTEM,"Started Mode %s", qPrintable(currentEditor->text()));
-	mm()->meshModified() = true;
+    if(mm()!=NULL)
+      mm()->meshModified() = true;
+    else assert(!iEdit->isSingleMeshEdit());
   }
 }
 
@@ -1114,9 +1119,9 @@ void GLArea::updateFps(float deltaTime)
 
 void GLArea::resetTrackBall()
 {
-	trackball.Reset();
+  trackball.Reset();
   float newScale= 3.0f/this->md()->bbox().Diag();
-	trackball.track.sca = newScale;
+  trackball.track.sca = newScale;
   trackball.track.tra =  -this->md()->bbox().Center();
   update();
 }
diff --git a/src/meshlab/glarea.h b/src/meshlab/glarea.h
index 5508d8640..6340cc0e7 100644
--- a/src/meshlab/glarea.h
+++ b/src/meshlab/glarea.h
@@ -124,7 +124,6 @@ public:
 	void saveSnapshot();
 	void setLightModel();
 	void setView();
-  void resetTrackBall();
   QList<QAction *> iDecoratorsList;
 
 	void setRenderer(MeshRenderInterface *rend, QAction *shader){	iRenderer = rend; currentShader = shader;}
@@ -139,7 +138,8 @@ public:
 	  
 public slots:
 	void updateTexture(); // slot for forcing the texture reload. 
-		
+	void resetTrackBall();
+
 	//slots for changing the draw rendering and texturing mode
 	void setDrawMode(vcg::GLW::DrawMode mode); 
 	void setColorMode(vcg::GLW::ColorMode mode);