diff --git a/data/blender/mitsuba/operators/__init__.py b/data/blender/mitsuba/operators/__init__.py
index 4f9f82f1..de2c38b9 100644
--- a/data/blender/mitsuba/operators/__init__.py
+++ b/data/blender/mitsuba/operators/__init__.py
@@ -125,7 +125,7 @@ class EXPORT_OT_mitsuba(bpy.types.Operator):
 	bl_idname = 'export.mitsuba'
 	bl_label = 'Export Mitsuba Scene (.xml)'
 
-	filename		= bpy.props.StringProperty(name='Target filename')
+	filename		= bpy.props.StringProperty(name='Target filename', subtype = 'FILE_PATH')
 	directory		= bpy.props.StringProperty(name='Target directory')
 	scene			= bpy.props.StringProperty(options={'HIDDEN'}, default='')
 
@@ -150,6 +150,9 @@ class EXPORT_OT_mitsuba(bpy.types.Operator):
 			mts_basename = os.path.join(
 				self.properties.directory,
 				self.properties.filename)
+			(path, ext) = os.path.splitext(mts_basename)
+			if ext == '.xml':
+				mts_basename = path
 			mts_dae_file = mts_basename + ".dae"
 			mts_xml_file = mts_basename + ".xml"
 			mts_adj_file = mts_basename + "_adjustments.xml"
@@ -206,7 +209,10 @@ class EXPORT_OT_mitsuba(bpy.types.Operator):
 			MtsLog("Caught exception: %s" % ''.join(elist))
 			return {'CANCELLED'}
 
-menu_func = lambda self, context: self.layout.operator("export.mitsuba", text="Export Mitsuba scene...")
+def menu_func(self, context):
+	default_path = os.path.splitext(os.path.basename(bpy.data.filepath))[0] + ".xml"
+	self.layout.operator("export.mitsuba", text="Export Mitsuba scene...").filename = default_path
+
 bpy.types.INFO_MT_file_export.append(menu_func)
 
 class MITSUBA_OT_material_slot_move(bpy.types.Operator):
diff --git a/include/mitsuba/render/kdtree.h b/include/mitsuba/render/kdtree.h
index 182d95b8..e3ec83a9 100644
--- a/include/mitsuba/render/kdtree.h
+++ b/include/mitsuba/render/kdtree.h
@@ -109,6 +109,10 @@ public:
 	void rayIntersectPacketIncoherent(const RayPacket4 &packet, 
 		const RayInterval4 &interval, Intersection4 &its, void *temp) const;
 #endif
+	
+	FINLINE size_type getPrimitiveCount() const {
+		return m_shapeMap[m_shapeMap.size()-1];
+	}
 
 	MTS_DECLARE_CLASS()
 protected:
@@ -149,10 +153,6 @@ protected:
 		}
 	}
 
-	FINLINE size_type getPrimitiveCount() const {
-		return m_shapeMap[m_shapeMap.size()-1];
-	}
- 
 	/// Temporarily holds some intersection information
 	struct IntersectionCache {
 		size_type shapeIndex;
diff --git a/src/qtgui/glwidget.cpp b/src/qtgui/glwidget.cpp
index e8bae554..11bcf1bb 100644
--- a/src/qtgui/glwidget.cpp
+++ b/src/qtgui/glwidget.cpp
@@ -50,7 +50,7 @@ GLWidget::GLWidget(QWidget *parent) :
 	connect(m_preview, SIGNAL(statusMessage(const QString &)), 
 		this, SIGNAL(statusMessage(const QString &)), Qt::QueuedConnection);
 	m_invertMouse = false;
-	m_navigationMode = EFlythroughFixedYaw;
+	m_navigationMode = EFlythrough;
 	m_ignoreMouseEvent = QPoint(0, 0);
 	m_didSetCursor = false;
 	m_softwareFallback = false;
@@ -406,7 +406,12 @@ void GLWidget::downloadFramebuffer() {
 		createdFramebuffer = true;
 	}
 
-	PreviewQueueEntry entry = m_preview->acquireBuffer();
+	PreviewQueueEntry entry = m_preview->acquireBuffer(1000);
+	if (entry.buffer == NULL) {
+		if (createdFramebuffer)
+			m_framebuffer->init();
+		return;
+	}
 
 	Point3i size = entry.buffer->getSize();
 	ref<Bitmap> sourceBitmap = new Bitmap(size.x, size.y, 128);
diff --git a/src/qtgui/logwidget.h b/src/qtgui/logwidget.h
index 0d9eec11..110994e1 100644
--- a/src/qtgui/logwidget.h
+++ b/src/qtgui/logwidget.h
@@ -38,7 +38,8 @@ public:
     void append(ELogLevel level, const std::string &message) {
 		if (!m_ignoreMessages) {
 			emit textMessage(level, QString::fromLatin1(message.c_str()));
-			floodCheck();
+			if (level >= EWarn)
+				floodCheck();
 		}
 	}
 
diff --git a/src/qtgui/mainwindow.cpp b/src/qtgui/mainwindow.cpp
index 3eb4a57e..ce28b02d 100644
--- a/src/qtgui/mainwindow.cpp
+++ b/src/qtgui/mainwindow.cpp
@@ -141,7 +141,7 @@ MainWindow::MainWindow(QWidget *parent) :
 	ui->glView->setInvertMouse(settings.value("invertMouse", false).toBool());
 	ui->glView->setMouseSensitivity(settings.value("mouseSensitivity", 3).toInt());
 	ui->glView->setNavigationMode((ENavigationMode) settings.value("navigationMode", 
-		EFlythroughFixedYaw).toInt());
+		EFlythrough).toInt());
 	m_searchPaths = settings.value("searchPaths", QStringList()).toStringList();
 	m_blockSize = settings.value("blockSize", 32).toInt();
 	m_listenPort = settings.value("listenPort", MTS_DEFAULT_PORT).toInt();
diff --git a/src/shapes/instance.cpp b/src/shapes/instance.cpp
index 36d8fa8f..c999f3be 100644
--- a/src/shapes/instance.cpp
+++ b/src/shapes/instance.cpp
@@ -48,6 +48,8 @@ public:
 	AABB getAABB() const {
 		const KDTree *kdtree = m_shapeGroup->getKDTree();
 		const AABB &aabb = kdtree->getAABB();
+		if (!aabb.isValid()) // the geometry group is empty
+			return aabb;
 		AABB result;
 		for (int i=0; i<8; ++i)
 			result.expandBy(m_objectToWorld(aabb.getCorner(i)));
diff --git a/src/shapes/shapegroup.cpp b/src/shapes/shapegroup.cpp
index 066cd904..1b62de33 100644
--- a/src/shapes/shapegroup.cpp
+++ b/src/shapes/shapegroup.cpp
@@ -22,6 +22,7 @@ MTS_NAMESPACE_BEGIN
 
 ShapeGroup::ShapeGroup(const Properties &props) : Shape(props) {
 	m_kdtree = new KDTree();
+	m_name = props.getID();
 }
 
 ShapeGroup::ShapeGroup(Stream *stream, InstanceManager *manager) 
@@ -85,6 +86,19 @@ bool ShapeGroup::isCompound() const {
 	return true;
 }
 
+std::string ShapeGroup::getName() const {
+	return m_name;
+}
+
+std::string ShapeGroup::toString() const {
+	std::ostringstream oss;
+		oss << "ShapeGroup[" << endl
+			<< "  name = \"" << m_name << "\", " << endl
+			<< "  primCount = " << m_kdtree->getPrimitiveCount() << endl
+			<< "]";
+	return oss.str();
+}
+
 MTS_IMPLEMENT_CLASS_S(ShapeGroup, false, Shape)
 MTS_EXPORT_PLUGIN(ShapeGroup, "Grouped geometry for instancing");
 MTS_NAMESPACE_END
diff --git a/src/shapes/shapegroup.h b/src/shapes/shapegroup.h
index a304701e..b313bcd2 100644
--- a/src/shapes/shapegroup.h
+++ b/src/shapes/shapegroup.h
@@ -59,9 +59,16 @@ public:
 	/// Return a pointer to the internal KD-tree
 	inline const KDTree *getKDTree() const { return m_kdtree.get(); }
 
+	/// Return the name of the geometry group
+	std::string getName() const;
+
+	/// Return a string representation
+	std::string toString() const;
+
 	MTS_DECLARE_CLASS()
 private:
 	ref<KDTree> m_kdtree;
+	std::string m_name;
 };
 
 MTS_NAMESPACE_END