use rna values because id-properties cant be edited/added during draw.

system_property_chart.py

-#
-# ***** BEGIN GPL LICENSE BLOCK *****
-#
+# ##### BEGIN GPL LICENSE BLOCK #####
 #
 #  This program is free software; you can redistribute it and/or
 #  modify it under the terms of the GNU General Public License
@@ -16,7 +14,9 @@
 #  along with this program; if not, write to the Free Software Foundation,
 #  Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 #
-# ***** END GPL LICENCE BLOCK *****
+# ##### END GPL LICENSE BLOCK #####
+
+# <pep8 compliant>
 
 bl_info = {
     "name": "Object Property Chart",
@@ -37,6 +37,7 @@ bl_info = {
 
 import bpy
 
+
 def _property_chart_data_get(self, context):
     # eg. context.active_object
     obj = eval("context.%s" % self.context_data_path_active)
@@ -73,10 +74,10 @@ def _property_chart_draw(self, context):
 
     id_storage = context.scene
 
-    strings = id_storage.get(self._PROP_STORAGE_ID)
+    strings = getattr(id_storage, self._PROP_STORAGE_ID)
 
-    if strings is None:
-        strings = id_storage[self._PROP_STORAGE_ID] = "data data.name"
+    # Collected all props, now display them all
+    layout = self.layout
 
     if strings:
 
@@ -107,10 +108,6 @@ def _property_chart_draw(self, context):
             if prop_found:
                 prop_all.append((obj, prop_pairs))
 
-
-        # Collected all props, now display them all
-        layout = self.layout
-
         row = layout.row(align=True)
 
         col = row.column()
@@ -139,7 +136,7 @@ def _property_chart_draw(self, context):
     # edit the display props
     col = layout.column()
     col.label(text="Object Properties")
-    col.prop(id_storage, '["%s"]' % self._PROP_STORAGE_ID, text="")
+    col.prop(id_storage, self._PROP_STORAGE_ID, text="")
 
 
 class View3DEditProps(bpy.types.Panel):
@@ -150,6 +147,7 @@ class View3DEditProps(bpy.types.Panel):
     bl_context = "objectmode"
 
     _PROP_STORAGE_ID = "view3d_edit_props"
+    _PROP_STORAGE_DEFAULT = "data data.name"
 
     # _property_chart_draw needs these
     context_data_path_active = "active_object"
@@ -165,6 +163,7 @@ class SequencerEditProps(bpy.types.Panel):
     bl_label = "Property Chart"
 
     _PROP_STORAGE_ID = "sequencer_edit_props"
+    _PROP_STORAGE_DEFAULT = "blend_type blend_alpha"
 
     # _property_chart_draw needs these
     context_data_path_active = "scene.sequence_editor.active_strip"
@@ -220,11 +219,24 @@ class CopyPropertyChart(bpy.types.Operator):
 
 
 def register():
-    pass
+    Scene = bpy.types.Scene
+
+    for cls in View3DEditProps, SequencerEditProps:
+        setattr(Scene,
+                cls._PROP_STORAGE_ID,
+                StringProperty(
+                    name="Scene Name",
+                    description="Name of POV-Ray scene to create. Empty name will use the name of the blend file.",
+                    default=cls._PROP_STORAGE_DEFAULT, maxlen=1024),
+                )
 
 
 def unregister():
-    pass
+    for cls in View3DEditProps, SequencerEditProps:
+        delattr(Scene,
+                cls._PROP_STORAGE_ID,
+                )
+
 
 if __name__ == "__main__":
     register()