diff -r 639a900999bc -r fdc285e5952f src/ldDocument.cc
--- a/src/ldDocument.cc	Thu Apr 17 21:51:59 2014 +0300
+++ b/src/ldDocument.cc	Fri Apr 18 18:46:25 2014 +0300
@@ -124,6 +124,7 @@
 // =============================================================================
 //
 LDDocument::LDDocument() :
+	m_flags (0),
 	m_gldata (new LDGLData)
 {
 	setImplicit (true);
@@ -141,7 +142,7 @@
 	// Remove this file from the list of files. This MUST be done FIRST, otherwise
 	// a ton of other functions will think this file is still valid when it is not!
 	g_loadedFiles.removeOne (this);
-
+	m_flags |= DOCF_IsBeingDestroyed;
 	m_history->setIgnoring (true);
 
 	// Clear everything from the model
@@ -471,7 +472,7 @@
 
 // =============================================================================
 //
-LDDocument* openDocument (QString path, bool search)
+LDDocument* openDocument (QString path, bool search, bool implicit)
 {
 	// Convert the file name to lowercase since some parts contain uppercase
 	// file names. I'll assume here that the library will always use lowercase
@@ -497,6 +498,7 @@
 		return null;
 
 	LDDocument* load = new LDDocument;
+	load->setImplicit (implicit);
 	load->setFullPath (fullpath);
 	load->setName (LDDocument::shortenName (load->fullPath()));
 	dprint ("name: %1 (%2)", load->name(), load->fullPath());
@@ -671,7 +673,7 @@
 		return;
 	}
 
-	LDDocument* file = openDocument (path, false);
+	LDDocument* file = openDocument (path, false, false);
 
 	if (not file)
 	{
@@ -1024,7 +1026,7 @@
 
 	// If it's not loaded, try open it
 	if (not doc)
-		doc = openDocument (filename, true);
+		doc = openDocument (filename, true, true);
 
 	return doc;
 }
@@ -1066,9 +1068,7 @@
 {
 	history()->add (new AddHistory (objects().size(), obj));
 	m_objects << obj;
-
-	if (obj->type() == LDObject::EVertex)
-		m_vertices << obj;
+	addKnownVerticesOf (obj);
 
 #ifdef DEBUG
 	if (not isImplicit())
@@ -1097,6 +1097,7 @@
 	m_objects.insert (pos, obj);
 	obj->setDocument (this);
 	g_win->R()->compileObject (obj);
+	addKnownVerticesOf (obj);
 
 #ifdef DEBUG
 	if (not isImplicit())
@@ -1106,14 +1107,61 @@
 
 // =============================================================================
 //
+void LDDocument::addKnownVerticesOf (LDObject* obj)
+{
+	if (isImplicit())
+		return;
+
+	if (obj->type() == LDObject::ESubfile)
+	{
+		for (LDObject* sub : static_cast<LDSubfile*> (obj)->inlineContents (true, false))
+		{
+			addKnownVerticesOf (sub);
+			sub->destroy();
+		}
+	}
+	else
+	{
+		for (int i = 0; i < obj->vertices(); ++i)
+			addKnownVertexReference (obj->vertex (i));
+	}
+}
+
+// =============================================================================
+//
+void LDDocument::removeKnownVerticesOf (LDObject* obj)
+{
+	if (isImplicit())
+		return;
+
+	if (obj->type() == LDObject::ESubfile)
+	{
+		for (LDObject* sub : static_cast<LDSubfile*> (obj)->inlineContents (true, false))
+		{
+			removeKnownVerticesOf (sub);
+			sub->destroy();
+		}
+	}
+	else
+	{
+		for (int i = 0; i < obj->vertices(); ++i)
+			removeKnownVertexReference (obj->vertex (i));
+	}
+}
+
+// =============================================================================
+//
 void LDDocument::forgetObject (LDObject* obj)
 {
 	int idx = obj->lineNumber();
 	obj->unselect();
 	assert (m_objects[idx] == obj);
 
-	if (not history()->isIgnoring())
+	if (not isImplicit() && not (flags() & DOCF_IsBeingDestroyed))
+	{
 		history()->add (new DelHistory (idx, obj));
+		removeKnownVerticesOf (obj);
+	}
 
 	m_objects.removeAt (idx);
 	obj->setDocument (null);
@@ -1121,6 +1169,44 @@
 
 // =============================================================================
 //
+void LDDocument::vertexChanged (const Vertex& a, const Vertex& b)
+{
+	removeKnownVertexReference (a);
+	addKnownVertexReference (b);
+}
+
+// =============================================================================
+//
+void LDDocument::addKnownVertexReference (const Vertex& a)
+{
+	if (isImplicit())
+		return;
+
+	auto it = m_vertices.find (a);
+
+	if (it == m_vertices.end())
+		m_vertices[a] = 1;
+	else
+		++it.value();
+}
+
+// =============================================================================
+//
+void LDDocument::removeKnownVertexReference (const Vertex& a)
+{
+	if (isImplicit())
+		return;
+
+	auto it = m_vertices.find (a);
+	assert (it != m_vertices.end());
+
+	// If there's no more references to a given vertex, it is to be removed.
+	if (--it.value() == 0)
+		m_vertices.erase (it);
+}
+
+// =============================================================================
+//
 bool safeToCloseAll()
 {
 	for (LDDocument* f : g_loadedFiles)
@@ -1144,9 +1230,11 @@
 		*m_history << new EditHistory (idx, oldcode, newcode);
 	}
 
+	removeKnownVerticesOf (m_objects[idx]);
 	m_objects[idx]->unselect();
 	m_objects[idx]->setDocument (null);
 	obj->setDocument (this);
+	addKnownVerticesOf (obj);
 	g_win->R()->compileObject (obj);
 	m_objects[idx] = obj;
 }
@@ -1354,8 +1442,8 @@
 	delete g_logoedStud;
 	delete g_logoedStud2;
 
-	g_logoedStud = openDocument ("stud-logo.dat", true);
-	g_logoedStud2 = openDocument ("stud2-logo.dat", true);
+	g_logoedStud = openDocument ("stud-logo.dat", true, true);
+	g_logoedStud2 = openDocument ("stud2-logo.dat", true, true);
 
 	print (LDDocument::tr ("Logoed studs loaded.\n"));
 }