diff --git a/content/fasoverlay.js.php b/content/fasoverlay.js.php
index fbd1883b0..2c7101b48 100644
--- a/content/fasoverlay.js.php
+++ b/content/fasoverlay.js.php
@@ -234,6 +234,13 @@ function onVerbandSelect(event)
 				treeStudent.database.RemoveDataSource(oldDatasources.getNext());
 			}
 
+			try
+			{
+				StudentTreeDatasource.removeXMLSinkObserver(StudentTreeSinkObserver);
+				treeStudent.builder.removeListener(StudentTreeListener);
+			}
+			catch(e)
+			{}
 			var rdfService = Components.classes["@mozilla.org/rdf/rdf-service;1"].getService(Components.interfaces.nsIRDFService);
 			StudentTreeDatasource = rdfService.GetDataSource(url);
 			StudentTreeDatasource.QueryInterface(Components.interfaces.nsIRDFRemoteDataSource);
@@ -271,6 +278,13 @@ function onVerbandSelect(event)
 				treeLV.database.RemoveDataSource(oldDatasources.getNext());
 			}
 
+			try
+			{
+				LvTreeDatasource.removeXMLSinkObserver(LvTreeSinkObserver);
+				treeLV.builder.removeListener(LvTreeListener);
+			}
+			catch(e)
+			{}
 			var rdfService1 = Components.classes["@mozilla.org/rdf/rdf-service;1"].getService(Components.interfaces.nsIRDFService);
 
 			LvTreeDatasource = rdfService1.GetDataSource(url);
@@ -308,6 +322,14 @@ function onVerbandSelect(event)
 				treeInt.database.RemoveDataSource(oldDatasources.getNext());
 			}
 
+			try
+			{
+				InteressentTreeDatasource.removeXMLSinkObserver(InteressentTreeSinkObserver);
+				treeInt.builder.removeListener(InteressentTreeListener);
+			}
+			catch(e)
+			{}
+			
 			var rdfService = Components.classes["@mozilla.org/rdf/rdf-service;1"].getService(Components.interfaces.nsIRDFService);
 			InteressentTreeDatasource = rdfService.GetDataSource(url);
 			InteressentTreeDatasource.QueryInterface(Components.interfaces.nsIRDFRemoteDataSource);
@@ -365,6 +387,14 @@ function onFachbereichSelect(event)
 			treeLV.database.RemoveDataSource(oldDatasources.getNext());
 		}
 
+		try
+		{
+			LvTreeDatasource.removeXMLSinkObserver(LvTreeSinkObserver);
+			treeLV.builder.removeListener(LvTreeListener);
+		}
+		catch(e)
+		{}
+			
 		var rdfService = Components.classes["@mozilla.org/rdf/rdf-service;1"].getService(Components.interfaces.nsIRDFService);
 		LvTreeDatasource = rdfService.GetDataSource(url);
 		LvTreeDatasource.QueryInterface(Components.interfaces.nsIRDFRemoteDataSource);
@@ -440,7 +470,15 @@ function onLektorSelect(event)
 		{
 			treeLV.database.RemoveDataSource(oldDatasources.getNext());
 		}
-
+		
+		try
+		{
+			LvTreeDatasource.removeXMLSinkObserver(LvTreeSinkObserver);
+			treeLV.builder.removeListener(LvTreeListener);
+		}
+		catch(e)
+		{}
+		
 		var rdfService = Components.classes["@mozilla.org/rdf/rdf-service;1"].getService(Components.interfaces.nsIRDFService);
 		LvTreeDatasource = rdfService.GetDataSource(url);
 		LvTreeDatasource.QueryInterface(Components.interfaces.nsIRDFRemoteDataSource);
diff --git a/content/student/interessentoverlay.js.php b/content/student/interessentoverlay.js.php
index c1bd1a0d9..7c33f308e 100644
--- a/content/student/interessentoverlay.js.php
+++ b/content/student/interessentoverlay.js.php
@@ -267,6 +267,7 @@ function InteressentTreeSelectInteressent()
 	   	}
 	}
 	document.getElementById('interessent-toolbar-label-anzahl').value='Anzahl: '+items;
+	//debug('items:'+items);
 }
 
 // ****
@@ -632,6 +633,13 @@ function InteressentAuswahl()
 	//Refresh damit die entfernten DS auch wirklich entfernt werden
 	doctree.builder.rebuild();
 
+	try
+	{
+		InteressentDokumentTreeNichtabgegebenDatasource.removeXMLSinkObserver(InteressentDokumentTreeNichtabgegebenSinkObserver);
+		doctree.builder.removeListener(InteressentDokumentTreeNichtabgegebenListener);
+	}
+	catch(e)
+	{}
 	var rdfService = Components.classes["@mozilla.org/rdf/rdf-service;1"].getService(Components.interfaces.nsIRDFService);
 	InteressentDokumentTreeNichtabgegebenDatasource = rdfService.GetDataSource(url);
 	InteressentDokumentTreeNichtabgegebenDatasource.QueryInterface(Components.interfaces.nsIRDFRemoteDataSource);
@@ -653,6 +661,13 @@ function InteressentAuswahl()
 	//Refresh damit die entfernten DS auch wirklich entfernt werden
 	doctree.builder.rebuild();
 
+	try
+	{
+		InteressentDokumentTreeAbgegebenDatasource.removeXMLSinkObserver(InteressentDokumentTreeAbgegebenSinkObserver);
+		doctree.builder.removeListener(InteressentDokumentTreeAbgegebenListener);
+	}
+	catch(e)
+	{}
 	var rdfService = Components.classes["@mozilla.org/rdf/rdf-service;1"].getService(Components.interfaces.nsIRDFService);
 	InteressentDokumentTreeAbgegebenDatasource = rdfService.GetDataSource(url);
 	InteressentDokumentTreeAbgegebenDatasource.QueryInterface(Components.interfaces.nsIRDFRemoteDataSource);
@@ -675,6 +690,13 @@ function InteressentAuswahl()
 	//Refresh damit die entfernten DS auch wirklich entfernt werden
 	kontotree.builder.rebuild();
 
+	try
+	{
+		InteressentKontoTreeDatasource.removeXMLSinkObserver(InteressentKontoTreeSinkObserver);
+		kontotree.builder.removeListener(InteressentKontoTreeListener);
+	}
+	catch(e)
+	{}
 	var rdfService = Components.classes["@mozilla.org/rdf/rdf-service;1"].getService(Components.interfaces.nsIRDFService);
 	InteressentKontoTreeDatasource = rdfService.GetDataSource(url);
 	InteressentKontoTreeDatasource.QueryInterface(Components.interfaces.nsIRDFRemoteDataSource);
@@ -1302,6 +1324,14 @@ function InteressentKontoFilter()
 	//Refresh damit die entfernten DS auch wirklich entfernt werden
 	kontotree.builder.rebuild();
 
+	try
+	{
+		InteressentKontoTreeDatasource.removeXMLSinkObserver(InteressentKontoTreeSinkObserver);
+		kontotree.builder.removeListener(InteressentKontoTreeListener);
+	}
+	catch(e)
+	{}
+	
 	InteressentKontoSelectBuchung = buchungsnr;
 
 	var rdfService = Components.classes["@mozilla.org/rdf/rdf-service;1"].getService(Components.interfaces.nsIRDFService);