diff --git a/resources/shaders/gouraud.vs b/resources/shaders/gouraud.vs
index a9f3f6118..17cc764e2 100644
--- a/resources/shaders/gouraud.vs
+++ b/resources/shaders/gouraud.vs
@@ -65,11 +65,15 @@ void main()
     intensity.y = 0.0;
 
     if (NdotL > 0.0)
-        intensity.y += LIGHT_TOP_SPECULAR * pow(max(dot(normal, reflect(-LIGHT_TOP_DIR, normal)), 0.0), LIGHT_TOP_SHININESS);
+    {    
+        vec3 position = (gl_ModelViewMatrix * gl_Vertex).xyz;
+        intensity.y += LIGHT_TOP_SPECULAR * pow(max(dot(-normalize(position), reflect(-LIGHT_TOP_DIR, normal)), 0.0), LIGHT_TOP_SHININESS);
+    }
 
     // Perform the same lighting calculation for the 2nd light source (no specular applied).
     NdotL = max(dot(normal, LIGHT_FRONT_DIR), 0.0);
-    intensity.x += NdotL * LIGHT_FRONT_DIFFUSE;
+    if (NdotL > 0.0)
+        intensity.x += NdotL * LIGHT_FRONT_DIFFUSE;
 
     // compute deltas for out of print volume detection (world coordinates)
     if (print_box.actived)
diff --git a/resources/shaders/variable_layer_height.vs b/resources/shaders/variable_layer_height.vs
index 4f98dfa56..5dd697063 100644
--- a/resources/shaders/variable_layer_height.vs
+++ b/resources/shaders/variable_layer_height.vs
@@ -35,12 +35,16 @@ void main()
     intensity.y = 0.0;
 
     if (NdotL > 0.0)
-        intensity.y += LIGHT_TOP_SPECULAR * pow(max(dot(normal, reflect(-LIGHT_TOP_DIR, normal)), 0.0), LIGHT_TOP_SHININESS);
+    {    
+        vec3 position = (gl_ModelViewMatrix * gl_Vertex).xyz;
+        intensity.y += LIGHT_TOP_SPECULAR * pow(max(dot(-normalize(position), reflect(-LIGHT_TOP_DIR, normal)), 0.0), LIGHT_TOP_SHININESS);
+    }
 
     // Perform the same lighting calculation for the 2nd light source (no specular)
     NdotL = max(dot(normal, LIGHT_FRONT_DIR), 0.0);
     
-    intensity.x += NdotL * LIGHT_FRONT_DIFFUSE;
+    if (NdotL > 0.0)
+        intensity.x += NdotL * LIGHT_FRONT_DIFFUSE;
 
     // Scaled to widths of the Z texture.
     if (object_max_z > 0.0)
diff --git a/src/slic3r/GUI/Field.cpp b/src/slic3r/GUI/Field.cpp
index a1a6583bc..c9e91bd95 100644
--- a/src/slic3r/GUI/Field.cpp
+++ b/src/slic3r/GUI/Field.cpp
@@ -1291,9 +1291,13 @@ void PointCtrl::set_value(const boost::any& value, bool change_event)
 boost::any& PointCtrl::get_value()
 {
 	double x, y;
-	x_textctrl->GetValue().ToDouble(&x);
-	y_textctrl->GetValue().ToDouble(&y);
-
+	if (!x_textctrl->GetValue().ToDouble(&x) ||
+		!y_textctrl->GetValue().ToDouble(&y))
+	{
+		set_value(m_value.empty() ? Vec2d(0.0, 0.0) : m_value, true);
+		show_error(m_parent, _L("Invalid numeric input."));
+	}
+	else
 	if (m_opt.min > x || x > m_opt.max ||
 		m_opt.min > y || y > m_opt.max)
 	{		
@@ -1303,7 +1307,7 @@ boost::any& PointCtrl::get_value()
 		if (y > m_opt.max) y = m_opt.max;
 		set_value(Vec2d(x, y), true);
 
-		show_error(m_parent, _(L("Input value is out of range")));
+		show_error(m_parent, _L("Input value is out of range"));
 	}
 
 	return m_value = Vec2d(x, y);