System Information
Windows 10 64 bit
Nvidia Quadro 600

Blender Version
Broken: d49985c

Exact steps for others to reproduce the error

When I execute the code below I get an error message in the console: "DAG zero... not allowed to happen!"
It does not seem to be very harmful at the first glimpse but maybe that 'should not happen'.

import bpy

object = bpy.data.objects.new("Test Object", None)
scene1 = bpy.context.scene
scene2 = bpy.data.scenes.new("Test Scene")

bpy.ops.wm.window_duplicate()
window1, window2 = bpy.data.window_managers[0].windows[:2]

window1.screen.scene = scene1
window2.screen.scene = scene2

scene1.objects.link(object)