Can't set flags on Gst.Pad from python

[Andrew Cook]

>>> import gi
>>> gi.require_version('Gst', '1.0')
>>> from gi.repository import Gst
>>> 
>>> pad = Gst.Pad.new("in", Gst.PadDirection.SINK)
>>> pad.flags #not an instance of PadFlags?
32
>>> Gst.PadFlags(pad.flags)
<flags GST_PAD_FLAG_FLUSHING of type GstPadFlags>
>>> 
>>> pad.flags = Gst.PadFlags.PROXY_CAPS
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
RuntimeError: unable to set value for field
>>> 
>>> pad.flags |= Gst.PadFlags.PROXY_CAPS
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
RuntimeError: unable to set value for field

version 1.2.1, current debian sid package

Am i missing something or is it just not possible yet?