diff --git a/include/mainwindow.h b/include/mainwindow.h
index d10feec..a8f14b2 100644
--- a/include/mainwindow.h
+++ b/include/mainwindow.h
@@ -11,6 +11,11 @@ namespace Ui {
 class MainWindow;
 }
 
+/** Responsibilities:
+  * - taking care of the menu and toolbars, file operations
+  * - displaying info in statusbar
+  * - handle content change
+  */
 class MainWindow : public QMainWindow
 {
     Q_OBJECT
diff --git a/src/graphwidget.cpp b/src/graphwidget.cpp
index db584ed..aa9fa55 100644
--- a/src/graphwidget.cpp
+++ b/src/graphwidget.cpp
@@ -812,6 +812,7 @@ void GraphWidget::addEdge(Node *source, Node *destination)
 
     if (destination == m_nodeList.first())
     {
+        setActiveNode(destination);
         emit notification(
                     tr("Root element cannot be an edge target."));
         return;
@@ -819,6 +820,7 @@ void GraphWidget::addEdge(Node *source, Node *destination)
 
     if (source->isConnected(destination))
     {
+        setActiveNode(destination);
         emit notification(
                     tr("There is already an edge between these two nodes."));
     }
@@ -842,8 +844,9 @@ void GraphWidget::addEdge(Node *source, Node *destination)
         // The Edge is secondary, because the Node already has a parent
         // (it is already a destination of another Edge)
         edge->setSecondary(sec);
-
         m_scene->addItem(edge);
+
+        setActiveNode(destination);
         emit contentChanged();
     }
 }
@@ -858,11 +861,13 @@ void GraphWidget::removeEdge(Node *source, Node *destination)
 
     if (!source->isConnected(destination))
     {
+        setActiveNode(destination);
         emit notification(tr("There no edge between these two nodes."));
     }
     else
     {
         source->deleteEdge(destination);
+        setActiveNode(destination);
         emit contentChanged();
     }
 }
@@ -893,7 +898,8 @@ void GraphWidget::setActiveNode(Node *node)
         m_activeNode->setBorder(false);
 
     m_activeNode = node;
-    m_activeNode->setBorder();
+    if (m_activeNode)
+        m_activeNode->setBorder();
 }
 
 // re-draw numbers
diff --git a/src/mainwindow.cpp b/src/mainwindow.cpp
index 2c0f6d9..d5549a2 100644
--- a/src/mainwindow.cpp
+++ b/src/mainwindow.cpp
@@ -53,6 +53,7 @@ void MainWindow::statusBarMsg(const QString &msg)
 
 void MainWindow::contentChanged(const bool& changed)
 {
+    // only care about the transitions
     if (m_contentChanged == false && changed == true)
     {
         setWindowTitle(windowTitle().prepend("* "));
@@ -276,12 +277,14 @@ void MainWindow::quit()
 
 void MainWindow::closeEvent(QCloseEvent * event)
 {
-    m_contentChanged && !closeFile() ? event->ignore() : event->accept();
+    m_contentChanged && !closeFile() ?
+                event->ignore() :
+                event->accept();
 }
 
 void MainWindow::keyPressEvent(QKeyEvent *event)
 {
-    // incative action does not listen to signals
+    // inactive action does not listen to signals
     if (event->modifiers() & Qt::ControlModifier)
     {
         if (event->key() == Qt::Key_M)