The following segfaults:

#######################################
from gi.repository import Gtk

model = Gtk.ListStore(object)
model.insert(0, row=[object()])

paths = []
def func(model, path, iter_, *args):
    paths.append(path)
model.foreach(func, None)

print paths[0]
#######################################

path is IN, ownership-transfer=None and doesn't seem to get copied.