GraphWindow needs "pos"

Creating a GraphWindow via win = GraphWindow(g, geometry=(400, 300), ...) leads to:

Exception AttributeError: "'GraphWindow' object has no attribute 'graph'" in <bound method GraphWindow.__del__ of <GraphWindow object at 0xa819f504 (uninitialized at 0x0)>> ignored
Traceback (most recent call last):
  File "example.py", line 76, in <module>
    vprops=vertexprop_dict)
TypeError: __init__() missing 1 required positional argument: 'pos'

As stated by the documentation "pos" should be optional (https://graph-tool.skewed.de/static/doc/draw.html#graph_tool.draw.GraphWindow):

pos : PropertyMap (optional, default: None).

Can someone tell where to get the argument to pass to "pos"? Important: I'm adding additional vertices after creating GraphWindow, using "pos=sfdp_layout(g)" leads to segmentation fault after adding some more.

Additional Infos: GTK+ 3.12.2 graph-tool 2.2.31