diff --git a/Modules/QtWidgets/src/QmitkDataStorageListModel.cpp b/Modules/QtWidgets/src/QmitkDataStorageListModel.cpp
index fa6c51590e..6f29902e20 100755
--- a/Modules/QtWidgets/src/QmitkDataStorageListModel.cpp
+++ b/Modules/QtWidgets/src/QmitkDataStorageListModel.cpp
@@ -1,336 +1,344 @@
 /*===================================================================
 
 The Medical Imaging Interaction Toolkit (MITK)
 
 Copyright (c) German Cancer Research Center,
 Division of Medical and Biological Informatics.
 All rights reserved.
 
 This software is distributed WITHOUT ANY WARRANTY; without
 even the implied warranty of MERCHANTABILITY or FITNESS FOR
 A PARTICULAR PURPOSE.
 
 See LICENSE.txt or http://www.mitk.org for details.
 
 ===================================================================*/
 
 #include "QmitkDataStorageListModel.h"
 
 //# Own includes
 // mitk
 #include "mitkStringProperty.h"
 
 //# Toolkit includes
 // itk
 #include "itkCommand.h"
 
 QmitkDataStorageListModel::QmitkDataStorageListModel(mitk::DataStorage* dataStorage,
                                                      mitk::NodePredicateBase::Pointer pred,
                                                      QObject* parent)
 :QAbstractListModel(parent),
  m_NodePredicate(nullptr),
  m_DataStorage(nullptr),
  m_BlockEvents(false)
 {
   this->SetPredicate(pred);
   this->SetDataStorage(dataStorage);
 }
 
 QmitkDataStorageListModel::~QmitkDataStorageListModel()
 {
   // set data storage to nullptr so that the event listener gets removed
   this->SetDataStorage(nullptr);
 }
 
 void QmitkDataStorageListModel::SetDataStorage(mitk::DataStorage::Pointer dataStorage)
 {
   if( m_DataStorage == dataStorage)
   {
     return;
   }
 
   // remove old listeners
   if(m_DataStorage != nullptr)
   {
     m_DataStorage->AddNodeEvent.RemoveListener(
       mitk::MessageDelegate1<QmitkDataStorageListModel, const mitk::DataNode*>(
         this, &QmitkDataStorageListModel::OnDataStorageNodeAdded));
 
     m_DataStorage->RemoveNodeEvent.RemoveListener(
       mitk::MessageDelegate1<QmitkDataStorageListModel, const mitk::DataNode*>(
         this, &QmitkDataStorageListModel::OnDataStorageNodeRemoved));
 
     m_DataStorage->RemoveObserver(m_DataStorageDeleteObserverTag);
     m_DataStorageDeleteObserverTag = 0;
   }
 
   m_DataStorage = dataStorage;
 
   if(m_DataStorage != nullptr)
   {
     // subscribe for node added/removed events
     m_DataStorage->AddNodeEvent.AddListener(
       mitk::MessageDelegate1<QmitkDataStorageListModel, const mitk::DataNode*>(
         this, &QmitkDataStorageListModel::OnDataStorageNodeAdded));
 
     m_DataStorage->RemoveNodeEvent.AddListener(
       mitk::MessageDelegate1<QmitkDataStorageListModel, const mitk::DataNode*>(
         this, &QmitkDataStorageListModel::OnDataStorageNodeRemoved));
 
     // add ITK delete listener on data storage
     itk::MemberCommand<QmitkDataStorageListModel>::Pointer deleteCommand =
     itk::MemberCommand<QmitkDataStorageListModel>::New();
     deleteCommand->SetCallbackFunction(this,
                                          &QmitkDataStorageListModel::OnDataStorageDeleted);
     m_DataStorageDeleteObserverTag = m_DataStorage->AddObserver(itk::DeleteEvent(), deleteCommand);
   }
 
   // reset/rebuild model
   reset();
 }
 
 Qt::ItemFlags QmitkDataStorageListModel::flags(const QModelIndex&) const
 {
   return Qt::ItemIsEnabled | Qt::ItemIsSelectable;
 }
 
 QVariant QmitkDataStorageListModel::data(const QModelIndex& index, int role) const
 {
   if(role == Qt::DisplayRole && index.isValid())
   {
     const mitk::DataNode* node = std::get<NODE>(m_NodesAndObserverTags.at(index.row()));
     return QVariant(QString::fromStdString(node->GetName()));
   }
   else
   {
     return QVariant();
   }
 }
 
 QVariant QmitkDataStorageListModel::headerData(int  /*section*/, Qt::Orientation  /*orientation*/, int  /*role*/) const
 {
   return QVariant(tr("Nodes"));
 }
 
 int QmitkDataStorageListModel::rowCount(const QModelIndex&  /*parent*/) const
 {
   return m_NodesAndObserverTags.size();
 }
 
 std::vector<mitk::DataNode*> QmitkDataStorageListModel::GetDataNodes() const
 {
   auto size = m_NodesAndObserverTags.size();
   std::vector<mitk::DataNode*> result(size);
   for (int i = 0; i < size; ++i)
   {
     result[i] = std::get<NODE>(m_NodesAndObserverTags[i]);
   }
   return result;
 }
 
 mitk::DataStorage* QmitkDataStorageListModel::GetDataStorage() const
 {
   return m_DataStorage;
 }
 
 
 void QmitkDataStorageListModel::SetPredicate(mitk::NodePredicateBase* pred)
 {
   m_NodePredicate = pred;
 
   // in a prior implementation the call to beginResetModel() been after reset().
   // Should this actually be the better order of calls, please document!
   QAbstractListModel::beginResetModel();
   reset();
   QAbstractListModel::endResetModel();
 }
 
 mitk::NodePredicateBase* QmitkDataStorageListModel::GetPredicate() const
 {
   return m_NodePredicate;
 }
 
 void QmitkDataStorageListModel::reset()
 {
   mitk::DataStorage::SetOfObjects::ConstPointer modelNodes;
 
   if ( m_DataStorage != nullptr )
   {
     if ( m_NodePredicate != nullptr )
     {
       modelNodes = m_DataStorage->GetSubset(m_NodePredicate);
     }
     else
     {
       modelNodes = m_DataStorage->GetAll();
     }
   }
 
   ClearInternalNodeList();
 
   // add all filtered nodes to our list
   if (modelNodes != nullptr)
   {
     for (auto& node : *modelNodes)
     {
         AddNodeToInternalList(node);
     }
   }
 }
 
 void QmitkDataStorageListModel::AddNodeToInternalList(mitk::DataNode* node)
 {
   if (m_DataStorage != nullptr)
   {
     itk::MemberCommand<QmitkDataStorageListModel>::Pointer nodeModifiedCommand;
     // add modified observer
     nodeModifiedCommand = itk::MemberCommand<QmitkDataStorageListModel>::New();
     nodeModifiedCommand->SetCallbackFunction(this, &QmitkDataStorageListModel::OnDataNodeModified);
     unsigned long nodeObserverTag =  node->AddObserver(itk::ModifiedEvent(), nodeModifiedCommand);
 
     itk::MemberCommand<QmitkDataStorageListModel>::Pointer dataModifiedCommand;
     unsigned long dataObserverTag = 0;
     // add modified observer
     if (node->GetData() != nullptr) {
       dataModifiedCommand = itk::MemberCommand<QmitkDataStorageListModel>::New();
       dataModifiedCommand->SetCallbackFunction(this, &QmitkDataStorageListModel::OnDataModified);
-      unsigned long dataObserverTag =  node->GetData()->AddObserver(itk::ModifiedEvent(), dataModifiedCommand);
+      dataObserverTag =  node->GetData()->AddObserver(itk::ModifiedEvent(), dataModifiedCommand);
     }
 
     m_NodesAndObserverTags.push_back( std::make_tuple(node, nodeObserverTag, dataObserverTag) );
   }
 }
 
 void QmitkDataStorageListModel::ClearInternalNodeList()
 {
   for(auto& iter : m_NodesAndObserverTags)
   {
-    std::get<NODE>(iter)->RemoveObserver(std::get<NODE_OBSERVER>(iter));
+    auto node = std::get<NODE>(iter);
+    if (node != nullptr)
+    {
+      node->RemoveObserver(std::get<NODE_OBSERVER>(iter));
+      if (node->GetData() != nullptr)
+      {
+        node->GetData()->RemoveObserver(std::get<DATA_OBSERVER>(iter));
+      }
+    }
   }
   m_NodesAndObserverTags.clear();
 }
 
 void QmitkDataStorageListModel::RemoveNodeFromInternalList(mitk::DataNode* node)
 {
   for(auto iter = m_NodesAndObserverTags.begin();
       iter != m_NodesAndObserverTags.end();
       ++iter)
   {
     if (std::get<NODE>(*iter) == node)
     {
       node->RemoveObserver(std::get<NODE_OBSERVER>(*iter));
       if (node->GetData() != nullptr)
       {
         node->GetData()->RemoveObserver(std::get<DATA_OBSERVER>(*iter));
       }
       m_NodesAndObserverTags.erase(iter); // invalidate iter
       break;
     }
   }
 }
 
 void QmitkDataStorageListModel::OnDataStorageNodeAdded( const mitk::DataNode* node )
 {
   // guarantee no recursions when a new node event is thrown
   if(!m_BlockEvents)
   {
     m_BlockEvents = true;
 
     // check if node should be added to the model
     bool addNode = true;
     if(m_NodePredicate && !m_NodePredicate->CheckNode(node))
       addNode = false;
 
     if(addNode)
     {
       int newIndex = m_NodesAndObserverTags.size();
       beginInsertRows(QModelIndex(), newIndex, newIndex);
       AddNodeToInternalList(const_cast<mitk::DataNode*>(node));
       endInsertRows();
     }
 
     m_BlockEvents = false;
   }
 }
 
 void QmitkDataStorageListModel::OnDataStorageNodeRemoved( const mitk::DataNode* node )
 {
   // guarantee no recursions when a new node event is thrown
   if(!m_BlockEvents)
   {
     m_BlockEvents = true;
 
     int row = 0;
     for(auto iter = m_NodesAndObserverTags.begin();
         iter != m_NodesAndObserverTags.end();
         ++iter, ++row)
     {
       if (std::get<NODE>(*iter) == node)
       {
         // node found, remove it
         beginRemoveRows(QModelIndex(), row, row);
         RemoveNodeFromInternalList(std::get<NODE>(*iter));
         endRemoveRows();
         break;
       }
     }
   }
 
   m_BlockEvents = false;
 }
 
 void QmitkDataStorageListModel::OnDataNodeModified( const itk::Object *caller, const itk::EventObject & /*event*/ )
 {
   if(m_BlockEvents) return;
 
   const mitk::DataNode* modifiedNode = dynamic_cast<const mitk::DataNode*>(caller);
   if(modifiedNode)
   {
     QModelIndex changedIndex = getIndex(modifiedNode);
     if (changedIndex.isValid())
     {
       emit dataChanged(changedIndex, changedIndex);
     }
   }
 }
 
 void QmitkDataStorageListModel::OnDataModified( const itk::Object *caller, const itk::EventObject & event )
 {
   OnDataNodeModified(caller, event); // until different implementation
 }
 
 
 void QmitkDataStorageListModel::OnDataStorageDeleted( const itk::Object *caller, const itk::EventObject & /*event*/ )
 {
   if(m_BlockEvents) return;
 
   // set data storage to nullptr -> empty model
   this->SetDataStorage(nullptr);
 }
 
 mitk::DataNode::Pointer QmitkDataStorageListModel::getNode( const QModelIndex &index ) const
 {
   if(index.isValid())
   {
     return std::get<NODE>(m_NodesAndObserverTags.at(index.row()));
   }
   else
   {
     return nullptr;
   }
 }
 
 QModelIndex QmitkDataStorageListModel::getIndex(const mitk::DataNode* node) const
 {
   int row = 0;
   for ( auto iter = m_NodesAndObserverTags.begin();
        iter != m_NodesAndObserverTags.end();
        ++iter, ++row )
   {
     if ( std::get<NODE>(*iter) == node )
     {
       return index(row);
     }
   }
   return QModelIndex();
 }