System Information
Windows 7, Nvidia Quadro 600

Blender Version
Broken: Blender 2.72 c6ab67b

Short description of error
I found another bug that is closely related to this one: T42619

Exact steps for others to reproduce the error

1. Open the text editor
2. Copy this script in a new text block

import bpy

class TestTree(bpy.types.NodeTree):
	bl_idname = "test_tree"
	bl_label = "Animation";
	bl_icon = "X"
	
	def update(self):
		bpy.context.scene.update()  # this is the only difference to the other bug
		
bpy.utils.register_class(TestTree)

bpy.data.node_groups.new("test", "test_tree").use_fake_user = True

3. Run the script
4. Save the current file (and leave Blender open!)
5. Open the just saved file -> crash